Feeling stupid

[Fred in Thailand]

I hope this is the right place

I have two tables, one for electric meter readings and one for water meter readings. each meter belongs to a unit. I want to be able to enter the new readings once a month and and have the old readings update for an amount used automatically.

As you can see my problem is with isolating the readings to the unit.

I think I should be using a script but i know just enough about this to be dangerous.

Any help will be greatly appreciated.

[Fred in Thailand]

Forgot this

R2_V2.zip