A single push-button on Model 303 causes the digital display in automatic rotation to show its three functions of: voltage, outside air temperature (Fahrenheit), outside air temperature (Centigrade). When the radio master switch of the aircraft is first turned on, The Model 303 always reads out the aircraft voltage to the nearest tenth of a volt. A code letter E indicates it is in the voltage function (EMF). To display outside air temperature in degrees Fahrenheit, the button is pressed, and the letter F appears to indicate this mode. The next press of the button displays C for outside temperature in degrees Centigrade.
The indicator remains in the mode selected as long as aircraft power is on. Any mode can be selected as fast as one can depress the switch. The mode selection will always sequence in the same manner (F C E) as indicated on the instruments face.
The digital outside temperature function replaces one of the most difficult-to-read instruments in the cockpit. The pilot may relate to outside air temp. in degrees Fahrenheit, then instantly change the display to degrees Centigrade for aircraft manual input, etc.
The voltage function of the indicator allows the pilot to monitor his electrical system precisely. By monitoring the voltage he can anticipate a low voltage condition, unlike a warning light which tells only that this condition has already occurred. Also, the pilot can know with more accuracy the amount of capacity remaining in the battery.
The voltage at which a battery is being charged is also of greatest importance, since over-charging can lead to excessive water loss and battery failure. In brief, the voltage function reveals valuable information which helps the pilot obtain more reliable and better service from the electrical system.