Column A contains employee numbers, column B contains numbers that
correspond to each employee.
In column C are numbers that come from another source and should match
up to those numbers in column B. In column D is the formula B-D. All
columns are in employee number order but sometimes I need to insert a
cell in column C to synchronise the rows - but when I do this it
upsets the formula in column D.

How can I change the formula in column D so that it always deducts
column B from D irrespective of how many cells I insert in column C?

Thanks