shorter Z movements (makes calibration faster)

Firmware/Marlin_main.cpp

@@ -4487,7 +4487,8 @@ if((eSoundMode==e_SOUND_MODE_LOUD)||(eSoundMode==e_SOUND_MODE_ONCE))
 			}
 
 			// Move Z up to MESH_HOME_Z_SEARCH.
-			current_position[Z_AXIS] = MESH_HOME_Z_SEARCH;
+			if((ix == 0) && (iy == 0)) current_position[Z_AXIS] = MESH_HOME_Z_SEARCH;
+			else current_position[Z_AXIS] += 2.f / nMeasPoints; //use relative movement from Z coordinate where PINDa triggered on previous point. This makes calibration faster.
 			plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], Z_LIFT_FEEDRATE, active_extruder);
 			st_synchronize();
 
@@ -4515,9 +4516,20 @@ if((eSoundMode==e_SOUND_MODE_LOUD)||(eSoundMode==e_SOUND_MODE_ONCE))
 				kill_message = _T(MSG_BED_LEVELING_FAILED_POINT_LOW);
 				break;
 			}
-			if (MESH_HOME_Z_SEARCH - current_position[Z_AXIS] < 0.1f) {
-				kill_message = _i("Bed leveling failed. Sensor disconnected or cable broken. Waiting for reset.");////MSG_BED_LEVELING_FAILED_PROBE_DISCONNECTED c=20 r=4
-				break;
+			if (MESH_HOME_Z_SEARCH - current_position[Z_AXIS] < 0.1f) { //broken cable or initial Z coordinate too low. Go to MESH_HOME_Z_SEARCH and repeat last step (z-probe) again to distinguish between these two cases.
+
+				current_position[Z_AXIS] = MESH_HOME_Z_SEARCH;
+				plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], Z_LIFT_FEEDRATE, active_extruder);
+				st_synchronize();
+
+				if (!find_bed_induction_sensor_point_z((has_z && mesh_point > 0) ? z0 - Z_CALIBRATION_THRESHOLD : -10.f, nProbeRetry)) { //if we have data from z calibration max allowed difference is 1mm for each point, if we dont have data max difference is 10mm from initial point  
+					kill_message = _T(MSG_BED_LEVELING_FAILED_POINT_LOW);
+					break;
+				}
+				if (MESH_HOME_Z_SEARCH - current_position[Z_AXIS] < 0.1f) {
+					kill_message = _i("Bed leveling failed. Sensor disconnected or cable broken. Waiting for reset.");////MSG_BED_LEVELING_FAILED_PROBE_DISCONNECTED c=20 r=4
+					break;
+				}
 			}
 			if (has_z && fabs(z0 - current_position[Z_AXIS]) > Z_CALIBRATION_THRESHOLD) { //if we have data from z calibration, max. allowed difference is 1mm for each point
 				kill_message = _i("Bed leveling failed. Sensor triggered too high. Waiting for reset.");////MSG_BED_LEVELING_FAILED_POINT_HIGH c=20 r=4

Firmware/mesh_bed_calibration.cpp

@@ -936,6 +936,7 @@ static inline void update_current_position_z()
 }
 
 // At the current position, find the Z stop.
+
 inline bool find_bed_induction_sensor_point_z(float minimum_z, uint8_t n_iter, int
 #ifdef SUPPORT_VERBOSITY
     verbosity_level