I am a novice using Crystal. I would appreciate help with what I believe requires a formula.
I need to display the difference between readings from month to month. I need to subtract the last month from the previous month and have been unable to figure out how to do it.

field    date     number
equip    1/1/14    136
equip    2/1/14    139 (display '3')
equip    3/1/14    140 (display '1')
                      Display total '4'
Thanks for any help.

Thank you!
How 'bout if I'm grouping on the equip field? I need the total for each month and grand total for each piece of equipment.

field    date     number
equip1    1/1/14   136
equip1   2/1/14    139 (display '3')
equip1    3/1/14   140 (display '1')
                      Display total '4'

field    date     number
equip2    1/1/14    95
equip2    2/1/14    96.60 (display '1.60')
equip2    3/1/14    97.20 (display '.60')
                      Display total '2.20'