percentage of change.

[(that - this)/that] x 100

A negative answer = increase % of change.

A positive answer = decreased % of change.

Let's say last week you at 5 lamb kebabs.

This week you at 2.5.

[(5-2.5)/5] x 100 = This week, you ate 50% less lamb kebabs than last week.

I might not be good at math*, but I've got the percentage of change down.

*I'm horrible at it.