cumulative sum query

Hello,

I have a query building a table named (idpap rus running rain), with columns id, yrdy, and ru_totalrain (the column to be summed, rainfall), please see the attachment.

Can someone suggest an faster query to calculate cumulative rainfall in 1, 2, 3, and 7 days in advance (or records in advance) of each yrdy, including the value on yrdy?

I've been using a select query with dlookups like the following and it takes forever...

RU_TOTALRAIN1D: DLookUp("[RU_TOTALRAIN]","idpap rus running rain","[ID]=" & [ID]-1)+[RU_TOTALRAIN]

Especially for the 7 day cumulative lookup...

Suggestions would be appreciated!

If this is running total scenario, MS has address the issue quite well here: http://support.microsoft.com/kb/290136