Mitsubishi SPD instructions on how to calculate the speed

Mitsubishi SPD instructions on how to calculate the speed?
N = (60 * D0 * 1000) / nt r / min
n What does it mean
Speed ​​detection command using the SPD,Its function number is FNC56,Speed ​​detection instruction is used in the detection unit time (time unit is ms) read from the specified number of pulses input into the relay (rising edge),And stored in the specified data register.
Command
ld m8000
spd k100 d100
dmul d100 k60 d128
ld x3
rst c235
N is a detected value per minute
N represents the number of pulses when the turntable revolution needs: supplement