depth=SQRT((pixvalue*unitlength*un itlength)/(255*4*TAN(halfangle*pi(&# 41;/180)*TAN(halfangle*pi()/180)))
I went into excel and figured out the equation necessary to calculate vbit cut depth given:
Unitlength=size of square that the vbit will drill into the center of.
halfangle=half of the included angle of the bit.
pixvalue = 0-255 (8 bit gray) where 0=white (no depth) and 255=max depth (circle cut fills whole unit square)
the pi()/180 on the angle calculations converts from degrees to radians necessary to get the tan function to work right with degree measurements.