"Rodger" wrote in message
news:gQMYi.33766$XF6.31540@edtnps90...

Uh, in all seriousness, why not use a taught snap line (or 20' piece of
string) and stretch it across the sub floor in various areas? Hold it up
3/16ths at either end and if it touches anywhere... If it doesn't touch
anywhere, drop it to the floor and if the floor drops below the line,
measure the drop.

- Rodger

Exactly might thought. The simplest possible way.