I just noticed a neat feature of the Rinnai 75LS.
If you hold down the UP arrow for a few seconds, followed by hitting the On/Off button, it will give you a GPM reading. The display only has enough room for 3 numbers, so a reading of 18, or example, would equal 1.8 gpm. I turned a bathroom tap on last night, full hot, the reading was 10 or 1.0 gpm. When my wife was showering this morning, it read 13 or 1.3 gpm, which sounds about right considering we have a 1.85 gpm shower head.
If you hit the down arrow, hold it for a few seconds, and then the power button, it gives a temperature reading of what is going out. While my wife was showering this morning, it stayed solid at 118. The unit itself was set to 120.