Calculating Differences between Records - Limitations?

Calculating Differences between Records - Limitations?

Hi,

I'm trying to understand if ZOHO can handle this.

Tanks have daily gauges - in Feet, Inches and Quarter Inches.

I'm wanting to calculate the differences between records to report on daily production.

I have created a formula field that takes (feet *12) + inches + quarter inches.

I'm not seeing a way to use pivot charts (or any other report) to calculate and graph these changes.  Am I am missing something simple?

Thanks,