As Hood says - a bit short of details.
You do not calibrate for different distances, or over different distances. In Config/Motor Tuning bottom left hand - Steps per, the question being asked is - How many pulses must Mach3 put out to move 1 unit - inches or millimeters. We assume you are in inches.
This figure MUST be calculated - not measured. It is simple.
If yours are 1.8 degree motors - 200 steps. On your drivers you have the ability to use microstepping - try 1/8 step as a good compromise - 200 x 8 = 1600. Any gearing between the motor and the leadscrew - mine is 3 to 1 - 1600 x 3 = 4800 and finally the pitch of the leadscrew. Don't try measuring - unless you bought it from a car boot sale , the seller will know what pitch it is and tell you. If you are using the original leadscrews on the machine, then the dials will tell you - mine are 10 rev to 1 inch. If it is a metric leadscrew then set the machine up in metric it is easier ( and use G20 to move back to Imperial)
Therefore my steps per is 4800 x 10 = 48,000. Enter this in steps per. Set your velocity to something modest to set off with - say 4 and your acceleration to 0.5 or at the most 1.
The way to measure if this is accurate is - make sure backlash compensation is OFF - (starting at x0y0) enter in the MDI line g0x0y1. The table will move 1 inch. Do not try and measure this, it was only to take up any backlash. Set up your measuring device (I use digital calipers) and zero them. Type in g0x0y2 and the table will move another inch. Measure this and it should be accurate to within (+ - )1 or 2 thou. You cannot measure better than that unless you have some very expensive measuring equipment.
If your answer is 1 inch, you are calibrated. If it is seriously astray then something is wrong and come back.
If you then type in g0x0y1 the table will return -1 inch, although it wont be 1 inch becasue of backlash. If you measure the shortfall this is backlash and can be entered in the backlash table.
Repeat for the other axis. (including the calculation of steps per if the set up is different).
You are calibrated. Switch on backlash compensation, set it at 50% and you are ready to roll.
You can go back to the Motor Tuning and gradually increase the velocity until the motors start to miss steps - you will hear this as a loud whining sound - set the velocity back a couple of steps to ensure this does not happen when you are using the machine in anger. Do the same with the acceleration.
On the Motor Tuning page -
after any alteration - click Save Axis Settings BEFORE you leave that page, otherwise the settings will revert to what was previously set.
Like the flag - has Independance been declared