How do I make a number, within a set ranges, in one field determine the value of another?

[KMarsh]

Hello,

I am not familiar with java script but this is what I’m trying to achieve. If I type a single to 3-digit value in form field "A" I want a predetermined value to appear in form field "B." Where the value in form field "A" lands deternines the value displayed in form field "B." My ranges are 900-750 = 3, 749-700=2, 699-660=1, 659-640=0, 639-0=-1.

I know how to write this formula in Excel. In cell "B1" type =IF(A1>749, 3, (IF(A1>699, 2, (IF(Cell>659, 1, (IF(A1>639, 0, -1))))))). This works great but I need the form in a PDF not Excel. 

Thank you for any help you can give me. 

[Nesa Nurani · Accepted solution]

As Validation script of field "A" use this:

var f = this.getField("B");
if(event.value >= 0 && event.value <= 639)
f.value = -1;
else if(event.value >= 640 && event.value <= 659)
f.value = 0;
else if(event.value >= 660 && event.value <= 699)
f.value = 1;
else if(event.value >= 700 && event.value <= 749)
f.value = 2;
else if(event.value >= 750 && event.value <= 900)
f.value = 3;

[KMarsh]

Thank you so much! This worked like a charm.