Newbie problem with Z movement in Hypercube setup

As a newbie to both 3D printing and coding I am stuck with an issue and don't know how to try to resolve it.
So far everything else seems to work but the Z movement is very odd. If I select Prepare from the menu and then Z movement. I can turn the knob on the control panel anticlockwise 1 step and nothing happens - then turn it back to zero and the table moves. Turn it clockwise one step (ie below zero even though the display stays at zero) and back to zero and it moves the other way. Multiple steps give greater movements but it is very erratic. I have no idea what to do next! Any help would be very much welcomed. I have a video of the behaviour as below. I'm using Marlin 1.1.9.
[drive.google.com]

Edited 1 time(s). Last edit at 03/27/2020 02:19PM by dthomson39.

One click should not move that distance, check your steps/mm for Z

Great thanks - I've looked through the config code and cannot find a steps/mm setting for Z - could you indicate where I might find it in the various .h files I'm not familiar with the coding yet

You can find this setting in Configuration.h

/**
 * Default Axis Steps Per Unit (steps/mm)
 * Override with M92
 *                                      X, Y, Z, E0 [, E1[, E2...]]
 */
#define DEFAULT_AXIS_STEPS_PER_UNIT   { 100, 100, 4000, 500 }