At 09:02 PM 5/16/2015, Keith Hughes wrote:
>Turn the propane on, and measure the difference in height of the
>water columns in the two legs.  If the "open" leg (not connected to
>the propane, and open to the atmosphere) water level is 11" above
>the "propane leg" water level, then the pressure is 11" water column
>(or WC or WG).

The system must be actually delivering propane while you
measure.  Otherwise the measured pressure will probably be artificially high.
Yrs,
d