Since ICL7106 give a visual range of -1999 to +1999 (2000 points), you need to fixe a voltage range to have the maximum of 1999 round to 2000 to simplify.
you want measuring 150v DC.
So the immediate range above 150v is 200v.
You need to do a input attenuators, so when you put 200v you need have 200mv to the input of the ICL7106.
You need have to activate the good decimal point on the LCD according visual range.
On range 200v with 2000 pts you have the visual range 199.9 v, so the decimal point must be activated after the first digit.
with other range, it is the same principe:
range 0-2v : max 1999 mv or 1.999 v
range 0-20v : max 19.99 v
range 0-200v : max 199.9 v
range 2000 v : max 1999 v
Here a link this some formulas to calculate the value for R1 and R2 resistor divisor.
Near "Input Attenuators"http://www.eidusa.com/Electronics_DPVM.htm