Add automatic river gauge. After dialing the Potomac...

Add automatic river gauge. After dialing the Potomac River Gauge, A.L. King, U.S. Weather Bureau observer, waits for the first buzz, then sets his stop watch which continues until the buzz signal is again heard then he stops the watch. The time interval between the two signals is converted into the gauge height by dividing the number of seconds in the interval by 30 as gauge height above a field zero point is represented 8/30 seconds for each vertical foot of water, 4/9/38