New Calculation Needed

[Tremor]

Hi there. I wonder if anyone can help with a new column I need in a report.
Below is a screenshot of how the report is now.

What I need is a fourth column that gives a running total for each customer every month.

Take for example, Sumesco food - they ordered 72 tonnes in May, and 48 tonnes in June - I'd like the fourth column to add each months totals up as it goes along, so next to Sumesco's tonnage in June, it should now also say 120 - which is May and Junes combined.

And I'd like it to continue to do it every subsequent month.

Hope I explained it ok!

 

[Uncle Gizmo]

I think you will find what you want here:
Rogers Access Library --- Excellent compendium of Access 2000 routines from Roger Carlson.

In this example it's called a "running sum" I think that's what you're after.