Multiple dives & average depth function?

[watchmanjc]

I do most of my diving from local boats, and never log more than 3 dives in a day as a rule.

I do not have a computer, but my dive watch (Casio sea pathfinder) has an average depth function.

When filling out my log, computing pressure groups on a square dive, using max depth obviously puts me at a disadvantage for multiple dives and nitrogen loading.

Is it safe to compute this using the average depth measurement form the dive?

What is the purpose of the average depth function?

Thanks All

Watchmanjc