Is it necessary to calculate exact distances ahead of time?

Is it necessary to calculate exact distances ahead of time?
You could take the time to calculate exact distances, but if time allows, you can adjust values in the program until you experimentally determine the required values.
Adjusting for a straight line
FOR Counter = 1 TO 122
PULSOUT 13, 850
PULSOUT 12, 650
PAUSE 20
NEXT
Adjusting for a left turn
FOR Counter = 1 TO 15
PULSOUT 13, 750 ‘Stop the left wheel
PULSOUT 12, 650 ‘Move right wheel CW at full speed
PAUSE 20
NEXT

You could take the time to calculate exact distances, but if time allows, you can adjust values in the program until you experimentally determine the required values.