Problem in Tension/compression

[precision]

Sir my plan is,

When motor's pully moves 68 turns then Screw( worm gear ) turn 1 time.
Screw = 6 TPI ( then plateform moves 1 inch = 25.40 mm )
so 1 turn of screw = 25.40/6 = 4.233333 mm.
so 68 turns of pully = 4.233 mm
so 1 turn of pully = 4.233/68 = 0.062205882 mm

I will attach encoder of 6 PPR direct to motor pully.

code
pitch var word
pitch = 10368 ; (62208 / 6 = 10368)
dummy var word

loop: dummy = (pitch * ABS(lastw0))
w1 = div32 10000

so w1 = .01 mm least count
motor's 68 turns = encoder's 408 turns (10368 * 408 )/10000

so plateform moves 4.230 mm

This is my calculation

.