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diff --git a/Marlin/src/gcode/calibrate/G33.cpp b/Marlin/src/gcode/calibrate/G33.cpp
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+++ b/Marlin/src/gcode/calibrate/G33.cpp
@@ -0,0 +1,648 @@
+/**
+ * Marlin 3D Printer Firmware
+ * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "../../inc/MarlinConfig.h"
+
+#if ENABLED(DELTA_AUTO_CALIBRATION)
+
+#include "../gcode.h"
+#include "../../module/delta.h"
+#include "../../module/motion.h"
+#include "../../module/stepper.h"
+#include "../../module/endstops.h"
+#include "../../lcd/marlinui.h"
+
+#if HAS_BED_PROBE
+  #include "../../module/probe.h"
+#endif
+
+#if HAS_MULTI_HOTEND
+  #include "../../module/tool_change.h"
+#endif
+
+#if HAS_LEVELING
+  #include "../../feature/bedlevel/bedlevel.h"
+#endif
+
+constexpr uint8_t _7P_STEP = 1,              // 7-point step - to change number of calibration points
+                  _4P_STEP = _7P_STEP * 2,   // 4-point step
+                  NPP      = _7P_STEP * 6;   // number of calibration points on the radius
+enum CalEnum : char {                        // the 7 main calibration points - add definitions if needed
+  CEN      = 0,
+  __A      = 1,
+  _AB      = __A + _7P_STEP,
+  __B      = _AB + _7P_STEP,
+  _BC      = __B + _7P_STEP,
+  __C      = _BC + _7P_STEP,
+  _CA      = __C + _7P_STEP,
+};
+
+#define LOOP_CAL_PT(VAR, S, N) for (uint8_t VAR=S; VAR<=NPP; VAR+=N)
+#define F_LOOP_CAL_PT(VAR, S, N) for (float VAR=S; VAR<NPP+0.9999; VAR+=N)
+#define I_LOOP_CAL_PT(VAR, S, N) for (float VAR=S; VAR>CEN+0.9999; VAR-=N)
+#define LOOP_CAL_ALL(VAR) LOOP_CAL_PT(VAR, CEN, 1)
+#define LOOP_CAL_RAD(VAR) LOOP_CAL_PT(VAR, __A, _7P_STEP)
+#define LOOP_CAL_ACT(VAR, _4P, _OP) LOOP_CAL_PT(VAR, _OP ? _AB : __A, _4P ? _4P_STEP : _7P_STEP)
+
+TERN_(HAS_MULTI_HOTEND, const uint8_t old_tool_index = active_extruder);
+
+float lcd_probe_pt(const xy_pos_t &xy);
+
+void ac_home() {
+  endstops.enable(true);
+  home_delta();
+  endstops.not_homing();
+}
+
+void ac_setup(const bool reset_bed) {
+  TERN_(HAS_MULTI_HOTEND, tool_change(0, true));
+
+  planner.synchronize();
+  remember_feedrate_scaling_off();
+
+  #if HAS_LEVELING
+    if (reset_bed) reset_bed_level(); // After full calibration bed-level data is no longer valid
+  #endif
+}
+
+void ac_cleanup(TERN_(HAS_MULTI_HOTEND, const uint8_t old_tool_index)) {
+  TERN_(DELTA_HOME_TO_SAFE_ZONE, do_blocking_move_to_z(delta_clip_start_height));
+  TERN_(HAS_BED_PROBE, probe.stow());
+  restore_feedrate_and_scaling();
+  TERN_(HAS_MULTI_HOTEND, tool_change(old_tool_index, true));
+}
+
+void print_signed_float(PGM_P const prefix, const float &f) {
+  SERIAL_ECHOPGM("  ");
+  serialprintPGM(prefix);
+  SERIAL_CHAR(':');
+  if (f >= 0) SERIAL_CHAR('+');
+  SERIAL_ECHO_F(f, 2);
+}
+
+/**
+ *  - Print the delta settings
+ */
+static void print_calibration_settings(const bool end_stops, const bool tower_angles) {
+  SERIAL_ECHOPAIR(".Height:", delta_height);
+  if (end_stops) {
+    print_signed_float(PSTR("Ex"), delta_endstop_adj.a);
+    print_signed_float(PSTR("Ey"), delta_endstop_adj.b);
+    print_signed_float(PSTR("Ez"), delta_endstop_adj.c);
+  }
+  if (end_stops && tower_angles) {
+    SERIAL_ECHOPAIR("  Radius:", delta_radius);
+    SERIAL_EOL();
+    SERIAL_CHAR('.');
+    SERIAL_ECHO_SP(13);
+  }
+  if (tower_angles) {
+    print_signed_float(PSTR("Tx"), delta_tower_angle_trim.a);
+    print_signed_float(PSTR("Ty"), delta_tower_angle_trim.b);
+    print_signed_float(PSTR("Tz"), delta_tower_angle_trim.c);
+  }
+  if ((!end_stops && tower_angles) || (end_stops && !tower_angles)) { // XOR
+    SERIAL_ECHOPAIR("  Radius:", delta_radius);
+  }
+  SERIAL_EOL();
+}
+
+/**
+ *  - Print the probe results
+ */
+static void print_calibration_results(const float z_pt[NPP + 1], const bool tower_points, const bool opposite_points) {
+  SERIAL_ECHOPGM(".    ");
+  print_signed_float(PSTR("c"), z_pt[CEN]);
+  if (tower_points) {
+    print_signed_float(PSTR(" x"), z_pt[__A]);
+    print_signed_float(PSTR(" y"), z_pt[__B]);
+    print_signed_float(PSTR(" z"), z_pt[__C]);
+  }
+  if (tower_points && opposite_points) {
+    SERIAL_EOL();
+    SERIAL_CHAR('.');
+    SERIAL_ECHO_SP(13);
+  }
+  if (opposite_points) {
+    print_signed_float(PSTR("yz"), z_pt[_BC]);
+    print_signed_float(PSTR("zx"), z_pt[_CA]);
+    print_signed_float(PSTR("xy"), z_pt[_AB]);
+  }
+  SERIAL_EOL();
+}
+
+/**
+ *  - Calculate the standard deviation from the zero plane
+ */
+static float std_dev_points(float z_pt[NPP + 1], const bool _0p_cal, const bool _1p_cal, const bool _4p_cal, const bool _4p_opp) {
+  if (!_0p_cal) {
+    float S2 = sq(z_pt[CEN]);
+    int16_t N = 1;
+    if (!_1p_cal) { // std dev from zero plane
+      LOOP_CAL_ACT(rad, _4p_cal, _4p_opp) {
+        S2 += sq(z_pt[rad]);
+        N++;
+      }
+      return LROUND(SQRT(S2 / N) * 1000.0f) / 1000.0f + 0.00001f;
+    }
+  }
+  return 0.00001f;
+}
+
+/**
+ *  - Probe a point
+ */
+static float calibration_probe(const xy_pos_t &xy, const bool stow) {
+  #if HAS_BED_PROBE
+    return probe.probe_at_point(xy, stow ? PROBE_PT_STOW : PROBE_PT_RAISE, 0, true, false);
+  #else
+    UNUSED(stow);
+    return lcd_probe_pt(xy);
+  #endif
+}
+
+/**
+ *  - Probe a grid
+ */
+static bool probe_calibration_points(float z_pt[NPP + 1], const int8_t probe_points, const bool towers_set, const bool stow_after_each) {
+  const bool _0p_calibration      = probe_points == 0,
+             _1p_calibration      = probe_points == 1 || probe_points == -1,
+             _4p_calibration      = probe_points == 2,
+             _4p_opposite_points  = _4p_calibration && !towers_set,
+             _7p_calibration      = probe_points >= 3,
+             _7p_no_intermediates = probe_points == 3,
+             _7p_1_intermediates  = probe_points == 4,
+             _7p_2_intermediates  = probe_points == 5,
+             _7p_4_intermediates  = probe_points == 6,
+             _7p_6_intermediates  = probe_points == 7,
+             _7p_8_intermediates  = probe_points == 8,
+             _7p_11_intermediates = probe_points == 9,
+             _7p_14_intermediates = probe_points == 10,
+             _7p_intermed_points  = probe_points >= 4,
+             _7p_6_center         = probe_points >= 5 && probe_points <= 7,
+             _7p_9_center         = probe_points >= 8;
+
+  LOOP_CAL_ALL(rad) z_pt[rad] = 0.0f;
+
+  if (!_0p_calibration) {
+
+    const float dcr = delta_calibration_radius();
+
+    if (!_7p_no_intermediates && !_7p_4_intermediates && !_7p_11_intermediates) { // probe the center
+      const xy_pos_t center{0};
+      z_pt[CEN] += calibration_probe(center, stow_after_each);
+      if (isnan(z_pt[CEN])) return false;
+    }
+
+    if (_7p_calibration) { // probe extra center points
+      const float start  = _7p_9_center ? float(_CA) + _7P_STEP / 3.0f : _7p_6_center ? float(_CA) : float(__C),
+                  steps  = _7p_9_center ? _4P_STEP / 3.0f : _7p_6_center ? _7P_STEP : _4P_STEP;
+      I_LOOP_CAL_PT(rad, start, steps) {
+        const float a = RADIANS(210 + (360 / NPP) *  (rad - 1)),
+                    r = dcr * 0.1;
+        const xy_pos_t vec = { cos(a), sin(a) };
+        z_pt[CEN] += calibration_probe(vec * r, stow_after_each);
+        if (isnan(z_pt[CEN])) return false;
+     }
+      z_pt[CEN] /= float(_7p_2_intermediates ? 7 : probe_points);
+    }
+
+    if (!_1p_calibration) {  // probe the radius
+      const CalEnum start  = _4p_opposite_points ? _AB : __A;
+      const float   steps  = _7p_14_intermediates ? _7P_STEP / 15.0f : // 15r * 6 + 10c = 100
+                             _7p_11_intermediates ? _7P_STEP / 12.0f : // 12r * 6 +  9c = 81
+                             _7p_8_intermediates  ? _7P_STEP /  9.0f : //  9r * 6 + 10c = 64
+                             _7p_6_intermediates  ? _7P_STEP /  7.0f : //  7r * 6 +  7c = 49
+                             _7p_4_intermediates  ? _7P_STEP /  5.0f : //  5r * 6 +  6c = 36
+                             _7p_2_intermediates  ? _7P_STEP /  3.0f : //  3r * 6 +  7c = 25
+                             _7p_1_intermediates  ? _7P_STEP /  2.0f : //  2r * 6 +  4c = 16
+                             _7p_no_intermediates ? _7P_STEP :        //  1r * 6 +  3c = 9
+                             _4P_STEP;                                // .5r * 6 +  1c = 4
+      bool zig_zag = true;
+      F_LOOP_CAL_PT(rad, start, _7p_9_center ? steps * 3 : steps) {
+        const int8_t offset = _7p_9_center ? 2 : 0;
+        for (int8_t circle = 0; circle <= offset; circle++) {
+          const float a = RADIANS(210 + (360 / NPP) *  (rad - 1)),
+                      r = dcr * (1 - 0.1 * (zig_zag ? offset - circle : circle)),
+                      interpol = FMOD(rad, 1);
+          const xy_pos_t vec = { cos(a), sin(a) };
+          const float z_temp = calibration_probe(vec * r, stow_after_each);
+          if (isnan(z_temp)) return false;
+          // split probe point to neighbouring calibration points
+          z_pt[uint8_t(LROUND(rad - interpol + NPP - 1)) % NPP + 1] += z_temp * sq(cos(RADIANS(interpol * 90)));
+          z_pt[uint8_t(LROUND(rad - interpol))           % NPP + 1] += z_temp * sq(sin(RADIANS(interpol * 90)));
+        }
+        zig_zag = !zig_zag;
+      }
+      if (_7p_intermed_points)
+        LOOP_CAL_RAD(rad)
+          z_pt[rad] /= _7P_STEP / steps;
+
+      do_blocking_move_to_xy(0.0f, 0.0f);
+    }
+  }
+  return true;
+}
+
+/**
+ * kinematics routines and auto tune matrix scaling parameters:
+ * see https://github.com/LVD-AC/Marlin-AC/tree/1.1.x-AC/documentation for
+ *  - formulae for approximative forward kinematics in the end-stop displacement matrix
+ *  - definition of the matrix scaling parameters
+ */
+static void reverse_kinematics_probe_points(float z_pt[NPP + 1], abc_float_t mm_at_pt_axis[NPP + 1]) {
+  xyz_pos_t pos{0};
+
+  const float dcr = delta_calibration_radius();
+  LOOP_CAL_ALL(rad) {
+    const float a = RADIANS(210 + (360 / NPP) *  (rad - 1)),
+                r = (rad == CEN ? 0.0f : dcr);
+    pos.set(cos(a) * r, sin(a) * r, z_pt[rad]);
+    inverse_kinematics(pos);
+    mm_at_pt_axis[rad] = delta;
+  }
+}
+
+static void forward_kinematics_probe_points(abc_float_t mm_at_pt_axis[NPP + 1], float z_pt[NPP + 1]) {
+  const float r_quot = delta_calibration_radius() / delta_radius;
+
+  #define ZPP(N,I,A) (((1.0f + r_quot * (N)) / 3.0f) * mm_at_pt_axis[I].A)
+  #define Z00(I, A) ZPP( 0, I, A)
+  #define Zp1(I, A) ZPP(+1, I, A)
+  #define Zm1(I, A) ZPP(-1, I, A)
+  #define Zp2(I, A) ZPP(+2, I, A)
+  #define Zm2(I, A) ZPP(-2, I, A)
+
+  z_pt[CEN] = Z00(CEN, a) + Z00(CEN, b) + Z00(CEN, c);
+  z_pt[__A] = Zp2(__A, a) + Zm1(__A, b) + Zm1(__A, c);
+  z_pt[__B] = Zm1(__B, a) + Zp2(__B, b) + Zm1(__B, c);
+  z_pt[__C] = Zm1(__C, a) + Zm1(__C, b) + Zp2(__C, c);
+  z_pt[_BC] = Zm2(_BC, a) + Zp1(_BC, b) + Zp1(_BC, c);
+  z_pt[_CA] = Zp1(_CA, a) + Zm2(_CA, b) + Zp1(_CA, c);
+  z_pt[_AB] = Zp1(_AB, a) + Zp1(_AB, b) + Zm2(_AB, c);
+}
+
+static void calc_kinematics_diff_probe_points(float z_pt[NPP + 1], abc_float_t delta_e, const float delta_r, abc_float_t delta_t) {
+  const float z_center = z_pt[CEN];
+  abc_float_t diff_mm_at_pt_axis[NPP + 1], new_mm_at_pt_axis[NPP + 1];
+
+  reverse_kinematics_probe_points(z_pt, diff_mm_at_pt_axis);
+
+  delta_radius += delta_r;
+  delta_tower_angle_trim += delta_t;
+  recalc_delta_settings();
+  reverse_kinematics_probe_points(z_pt, new_mm_at_pt_axis);
+
+  LOOP_CAL_ALL(rad) diff_mm_at_pt_axis[rad] -= new_mm_at_pt_axis[rad] + delta_e;
+  forward_kinematics_probe_points(diff_mm_at_pt_axis, z_pt);
+
+  LOOP_CAL_RAD(rad) z_pt[rad] -= z_pt[CEN] - z_center;
+  z_pt[CEN] = z_center;
+
+  delta_radius -= delta_r;
+  delta_tower_angle_trim -= delta_t;
+  recalc_delta_settings();
+}
+
+static float auto_tune_h() {
+  const float r_quot = delta_calibration_radius() / delta_radius;
+  return RECIPROCAL(r_quot / (2.0f / 3.0f));  // (2/3)/CR
+}
+
+static float auto_tune_r() {
+  constexpr float diff = 0.01f, delta_r = diff;
+  float r_fac = 0.0f, z_pt[NPP + 1] = { 0.0f };
+  abc_float_t delta_e = { 0.0f }, delta_t = { 0.0f };
+
+  calc_kinematics_diff_probe_points(z_pt, delta_e, delta_r, delta_t);
+  r_fac = -(z_pt[__A] + z_pt[__B] + z_pt[__C] + z_pt[_BC] + z_pt[_CA] + z_pt[_AB]) / 6.0f;
+  r_fac = diff / r_fac / 3.0f; // 1/(3*delta_Z)
+  return r_fac;
+}
+
+static float auto_tune_a() {
+  constexpr float diff = 0.01f, delta_r = 0.0f;
+  float a_fac = 0.0f, z_pt[NPP + 1] = { 0.0f };
+  abc_float_t delta_e = { 0.0f }, delta_t = { 0.0f };
+
+  delta_t.reset();
+  LOOP_XYZ(axis) {
+    delta_t[axis] = diff;
+    calc_kinematics_diff_probe_points(z_pt, delta_e, delta_r, delta_t);
+    delta_t[axis] = 0;
+    a_fac += z_pt[uint8_t((axis * _4P_STEP) - _7P_STEP + NPP) % NPP + 1] / 6.0f;
+    a_fac -= z_pt[uint8_t((axis * _4P_STEP) + 1 + _7P_STEP)] / 6.0f;
+  }
+  a_fac = diff / a_fac / 3.0f; // 1/(3*delta_Z)
+  return a_fac;
+}
+
+/**
+ * G33 - Delta '1-4-7-point' Auto-Calibration
+ *       Calibrate height, z_offset, endstops, delta radius, and tower angles.
+ *
+ * Parameters:
+ *
+ *   Pn  Number of probe points:
+ *      P0       Normalizes calibration.
+ *      P1       Calibrates height only with center probe.
+ *      P2       Probe center and towers. Calibrate height, endstops and delta radius.
+ *      P3       Probe all positions: center, towers and opposite towers. Calibrate all.
+ *      P4-P10   Probe all positions at different intermediate locations and average them.
+ *
+ *   T   Don't calibrate tower angle corrections
+ *
+ *   Cn.nn  Calibration precision; when omitted calibrates to maximum precision
+ *
+ *   Fn  Force to run at least n iterations and take the best result
+ *
+ *   Vn  Verbose level:
+ *      V0  Dry-run mode. Report settings and probe results. No calibration.
+ *      V1  Report start and end settings only
+ *      V2  Report settings at each iteration
+ *      V3  Report settings and probe results
+ *
+ *   E   Engage the probe for each point
+ */
+void GcodeSuite::G33() {
+
+  const int8_t probe_points = parser.intval('P', DELTA_CALIBRATION_DEFAULT_POINTS);
+  if (!WITHIN(probe_points, 0, 10)) {
+    SERIAL_ECHOLNPGM("?(P)oints implausible (0-10).");
+    return;
+  }
+
+  const bool towers_set = !parser.seen('T');
+
+  const float calibration_precision = parser.floatval('C', 0.0f);
+  if (calibration_precision < 0) {
+    SERIAL_ECHOLNPGM("?(C)alibration precision implausible (>=0).");
+    return;
+  }
+
+  const int8_t force_iterations = parser.intval('F', 0);
+  if (!WITHIN(force_iterations, 0, 30)) {
+    SERIAL_ECHOLNPGM("?(F)orce iteration implausible (0-30).");
+    return;
+  }
+
+  const int8_t verbose_level = parser.byteval('V', 1);
+  if (!WITHIN(verbose_level, 0, 3)) {
+    SERIAL_ECHOLNPGM("?(V)erbose level implausible (0-3).");
+    return;
+  }
+
+  const bool stow_after_each = parser.seen('E');
+
+  const bool _0p_calibration      = probe_points == 0,
+             _1p_calibration      = probe_points == 1 || probe_points == -1,
+             _4p_calibration      = probe_points == 2,
+             _4p_opposite_points  = _4p_calibration && !towers_set,
+             _7p_9_center         = probe_points >= 8,
+             _tower_results       = (_4p_calibration && towers_set) || probe_points >= 3,
+             _opposite_results    = (_4p_calibration && !towers_set) || probe_points >= 3,
+             _endstop_results     = probe_points != 1 && probe_points != -1 && probe_points != 0,
+             _angle_results       = probe_points >= 3 && towers_set;
+  int8_t iterations = 0;
+  float test_precision,
+        zero_std_dev = (verbose_level ? 999.0f : 0.0f), // 0.0 in dry-run mode : forced end
+        zero_std_dev_min = zero_std_dev,
+        zero_std_dev_old = zero_std_dev,
+        h_factor, r_factor, a_factor,
+        r_old = delta_radius,
+        h_old = delta_height;
+
+  abc_pos_t e_old = delta_endstop_adj, a_old = delta_tower_angle_trim;
+
+  SERIAL_ECHOLNPGM("G33 Auto Calibrate");
+
+  const float dcr = delta_calibration_radius();
+
+  if (!_1p_calibration && !_0p_calibration) { // test if the outer radius is reachable
+    LOOP_CAL_RAD(axis) {
+      const float a = RADIANS(210 + (360 / NPP) *  (axis - 1));
+      if (!position_is_reachable(cos(a) * dcr, sin(a) * dcr)) {
+        SERIAL_ECHOLNPGM("?Bed calibration radius implausible.");
+        return;
+      }
+    }
+  }
+
+  // Report settings
+  PGM_P const checkingac = PSTR("Checking... AC");
+  serialprintPGM(checkingac);
+  if (verbose_level == 0) SERIAL_ECHOPGM(" (DRY-RUN)");
+  SERIAL_EOL();
+  ui.set_status_P(checkingac);
+
+  print_calibration_settings(_endstop_results, _angle_results);
+
+  ac_setup(!_0p_calibration && !_1p_calibration);
+
+  if (!_0p_calibration) ac_home();
+
+  do { // start iterations
+
+    float z_at_pt[NPP + 1] = { 0.0f };
+
+    test_precision = zero_std_dev_old != 999.0f ? (zero_std_dev + zero_std_dev_old) / 2.0f : zero_std_dev;
+    iterations++;
+
+    // Probe the points
+    zero_std_dev_old = zero_std_dev;
+    if (!probe_calibration_points(z_at_pt, probe_points, towers_set, stow_after_each)) {
+      SERIAL_ECHOLNPGM("Correct delta settings with M665 and M666");
+      return ac_cleanup(TERN_(HAS_MULTI_HOTEND, old_tool_index));
+    }
+    zero_std_dev = std_dev_points(z_at_pt, _0p_calibration, _1p_calibration, _4p_calibration, _4p_opposite_points);
+
+    // Solve matrices
+
+    if ((zero_std_dev < test_precision || iterations <= force_iterations) && zero_std_dev > calibration_precision) {
+
+      #if !HAS_BED_PROBE
+        test_precision = 0.0f; // forced end
+      #endif
+
+      if (zero_std_dev < zero_std_dev_min) {
+        // set roll-back point
+        e_old = delta_endstop_adj;
+        r_old = delta_radius;
+        h_old = delta_height;
+        a_old = delta_tower_angle_trim;
+      }
+
+      abc_float_t e_delta = { 0.0f }, t_delta = { 0.0f };
+      float r_delta = 0.0f;
+
+      /**
+       * convergence matrices:
+       * see https://github.com/LVD-AC/Marlin-AC/tree/1.1.x-AC/documentation for
+       *  - definition of the matrix scaling parameters
+       *  - matrices for 4 and 7 point calibration
+       */
+      #define ZP(N,I) ((N) * z_at_pt[I] / 4.0f) // 4.0 = divider to normalize to integers
+      #define Z12(I) ZP(12, I)
+      #define Z4(I) ZP(4, I)
+      #define Z2(I) ZP(2, I)
+      #define Z1(I) ZP(1, I)
+      #define Z0(I) ZP(0, I)
+
+      // calculate factors
+      if (_7p_9_center) calibration_radius_factor = 0.9f;
+      h_factor = auto_tune_h();
+      r_factor = auto_tune_r();
+      a_factor = auto_tune_a();
+      calibration_radius_factor = 1.0f;
+
+      switch (probe_points) {
+        case 0:
+          test_precision = 0.0f; // forced end
+          break;
+
+        case 1:
+          test_precision = 0.0f; // forced end
+          LOOP_XYZ(axis) e_delta[axis] = +Z4(CEN);
+          break;
+
+        case 2:
+          if (towers_set) { // see 4 point calibration (towers) matrix
+            e_delta.set((+Z4(__A) -Z2(__B) -Z2(__C)) * h_factor  +Z4(CEN),
+                        (-Z2(__A) +Z4(__B) -Z2(__C)) * h_factor  +Z4(CEN),
+                        (-Z2(__A) -Z2(__B) +Z4(__C)) * h_factor  +Z4(CEN));
+            r_delta   = (+Z4(__A) +Z4(__B) +Z4(__C) -Z12(CEN)) * r_factor;
+          }
+          else { // see 4 point calibration (opposites) matrix
+            e_delta.set((-Z4(_BC) +Z2(_CA) +Z2(_AB)) * h_factor  +Z4(CEN),
+                        (+Z2(_BC) -Z4(_CA) +Z2(_AB)) * h_factor  +Z4(CEN),
+                        (+Z2(_BC) +Z2(_CA) -Z4(_AB)) * h_factor  +Z4(CEN));
+            r_delta   = (+Z4(_BC) +Z4(_CA) +Z4(_AB) -Z12(CEN)) * r_factor;
+          }
+          break;
+
+        default: // see 7 point calibration (towers & opposites) matrix
+          e_delta.set((+Z2(__A) -Z1(__B) -Z1(__C) -Z2(_BC) +Z1(_CA) +Z1(_AB)) * h_factor  +Z4(CEN),
+                      (-Z1(__A) +Z2(__B) -Z1(__C) +Z1(_BC) -Z2(_CA) +Z1(_AB)) * h_factor  +Z4(CEN),
+                      (-Z1(__A) -Z1(__B) +Z2(__C) +Z1(_BC) +Z1(_CA) -Z2(_AB)) * h_factor  +Z4(CEN));
+          r_delta   = (+Z2(__A) +Z2(__B) +Z2(__C) +Z2(_BC) +Z2(_CA) +Z2(_AB) -Z12(CEN)) * r_factor;
+
+          if (towers_set) { // see 7 point tower angle calibration (towers & opposites) matrix
+            t_delta.set((+Z0(__A) -Z4(__B) +Z4(__C) +Z0(_BC) -Z4(_CA) +Z4(_AB) +Z0(CEN)) * a_factor,
+                        (+Z4(__A) +Z0(__B) -Z4(__C) +Z4(_BC) +Z0(_CA) -Z4(_AB) +Z0(CEN)) * a_factor,
+                        (-Z4(__A) +Z4(__B) +Z0(__C) -Z4(_BC) +Z4(_CA) +Z0(_AB) +Z0(CEN)) * a_factor);
+          }
+          break;
+      }
+      delta_endstop_adj += e_delta;
+      delta_radius += r_delta;
+      delta_tower_angle_trim += t_delta;
+    }
+    else if (zero_std_dev >= test_precision) {
+      // roll back
+      delta_endstop_adj = e_old;
+      delta_radius = r_old;
+      delta_height = h_old;
+      delta_tower_angle_trim = a_old;
+    }
+
+    if (verbose_level != 0) {                                    // !dry run
+
+      // Normalize angles to least-squares
+      if (_angle_results) {
+        float a_sum = 0.0f;
+        LOOP_XYZ(axis) a_sum += delta_tower_angle_trim[axis];
+        LOOP_XYZ(axis) delta_tower_angle_trim[axis] -= a_sum / 3.0f;
+      }
+
+      // adjust delta_height and endstops by the max amount
+      const float z_temp = _MAX(delta_endstop_adj.a, delta_endstop_adj.b, delta_endstop_adj.c);
+      delta_height -= z_temp;
+      LOOP_XYZ(axis) delta_endstop_adj[axis] -= z_temp;
+    }
+    recalc_delta_settings();
+    NOMORE(zero_std_dev_min, zero_std_dev);
+
+    // print report
+
+    if (verbose_level == 3)
+      print_calibration_results(z_at_pt, _tower_results, _opposite_results);
+
+    if (verbose_level != 0) { // !dry run
+      if ((zero_std_dev >= test_precision && iterations > force_iterations) || zero_std_dev <= calibration_precision) { // end iterations
+        SERIAL_ECHOPGM("Calibration OK");
+        SERIAL_ECHO_SP(32);
+        #if HAS_BED_PROBE
+          if (zero_std_dev >= test_precision && !_1p_calibration && !_0p_calibration)
+            SERIAL_ECHOPGM("rolling back.");
+          else
+        #endif
+          {
+            SERIAL_ECHOPAIR_F("std dev:", zero_std_dev_min, 3);
+          }
+        SERIAL_EOL();
+        char mess[21];
+        strcpy_P(mess, PSTR("Calibration sd:"));
+        if (zero_std_dev_min < 1)
+          sprintf_P(&mess[15], PSTR("0.%03i"), (int)LROUND(zero_std_dev_min * 1000.0f));
+        else
+          sprintf_P(&mess[15], PSTR("%03i.x"), (int)LROUND(zero_std_dev_min));
+        ui.set_status(mess);
+        print_calibration_settings(_endstop_results, _angle_results);
+        SERIAL_ECHOLNPGM("Save with M500 and/or copy to Configuration.h");
+      }
+      else { // !end iterations
+        char mess[15];
+        if (iterations < 31)
+          sprintf_P(mess, PSTR("Iteration : %02i"), (unsigned int)iterations);
+        else
+          strcpy_P(mess, PSTR("No convergence"));
+        SERIAL_ECHO(mess);
+        SERIAL_ECHO_SP(32);
+        SERIAL_ECHOLNPAIR_F("std dev:", zero_std_dev, 3);
+        ui.set_status(mess);
+        if (verbose_level > 1)
+          print_calibration_settings(_endstop_results, _angle_results);
+      }
+    }
+    else { // dry run
+      PGM_P const enddryrun = PSTR("End DRY-RUN");
+      serialprintPGM(enddryrun);
+      SERIAL_ECHO_SP(35);
+      SERIAL_ECHOLNPAIR_F("std dev:", zero_std_dev, 3);
+
+      char mess[21];
+      strcpy_P(mess, enddryrun);
+      strcpy_P(&mess[11], PSTR(" sd:"));
+      if (zero_std_dev < 1)
+        sprintf_P(&mess[15], PSTR("0.%03i"), (int)LROUND(zero_std_dev * 1000.0f));
+      else
+        sprintf_P(&mess[15], PSTR("%03i.x"), (int)LROUND(zero_std_dev));
+      ui.set_status(mess);
+    }
+    ac_home();
+  }
+  while (((zero_std_dev < test_precision && iterations < 31) || iterations <= force_iterations) && zero_std_dev > calibration_precision);
+
+  ac_cleanup(TERN_(HAS_MULTI_HOTEND, old_tool_index));
+}
+
+#endif // DELTA_AUTO_CALIBRATION