reverted to upstream

Marlin/Configuration_adv.h

 //homing hits the endstop, then retracts by this distance, before it tries to slowly bump again:
 #define X_HOME_RETRACT_MM 5
 #define Y_HOME_RETRACT_MM 5
-#define Z_HOME_RETRACT_MM 5
+#define Z_HOME_RETRACT_MM 2
 //#define QUICK_HOME  //if this is defined, if both x and y are to be homed, a diagonal move will be performed initially.
 
 #define AXIS_RELATIVE_MODES {false, false, false, false}
 #define DEFAULT_MINSEGMENTTIME        20000
 
 // If defined the movements slow down when the look ahead buffer is only half full
-// #define SLOWDOWN // JFR - important, was enabled!!
+#define SLOWDOWN
 
 // Frequency limit
 // See nophead's blog for more info

Marlin/example_configurations/delta/Configuration.h

 // and processor overload (too many expensive sqrt calls).
 #define DELTA_SEGMENTS_PER_SECOND 200
 
+// NOTE NB all values for DELTA_* values MUST be floating point, so always have a decimal point in them
+
 // Center-to-center distance of the holes in the diagonal push rods.
 #define DELTA_DIAGONAL_ROD 250.0 // mm