I worked for Simpson and that same model was made well into the 1980's. If you look in the battery compartment area you might see the quality control inspector's stamp. If the stamp in in the shape of the state of Wisconsin, your meter was built in Eagle River, WI and the 4 small numbers represent the week and year of manufacture.
lower scale is indeed Fahrenheit. most likely it has a different setting like a volt meter to measure higher temps. note how 212 deg stands out, boiling temp of water at sea level. one cool unit you have there!