"John Ball" wrote:
Not sure whether =IF function is the correct on to use,
but I need to test on values in column A, to see if the
value is 1500 more (+) or less (-) than values in column B.
I would also like to get an output in column C, so that
if the result is "true" then a number "3" can be attributed
for coding purposes

Try:

=IF(ABS(A2-B2)<=1500,3,"")

You neglect to say what you want if column A is not within 1500 of column B.
I opted for the null string (""). Replace "" with something else if you
wish.