Are Old Manhole Plans in Decimal Feet or Feet/Inches?

Looking at old sewer plans: I've been stumped on the measurement unit for Manhole depth. Sometimes for these old plans it seems that the manhole depth is written with double primes (") in between 2 numbers but at the bottom. Im not sure If this means the number is written in feet and inches or in decimal feet (tenths). 

If anyone knows how to read old sewer plans (pre 1940s) please let me know.

Also these plans often gives elevation in decimal feet (I assume) in red. The depth is in black. In the examples I attached you can see that sometimes the primes are there and other times the denotation isn't as invasive on the measurement.