I need to show the difference between costings for last month, compared
with this month.

For example, last month a particular costing showed a profit of $100.
This month is showing a loss of -$200. I need to show that this month
the difference between the costings is therefore -$100, or, $100
dollars less than last month.

Can anyone offer me the formula to do this?

Sneaky second question!... it would be useful to display, in the above
example, "$100 less", rather than "-$100". Can this be done?

Many thanks