Probably a simple auto flash with GN38 in meters at ASA100. Look at the top scale, turn to put in your ASA film speed, the different automodes (most often two different modes) are usually color coded on the scale, you'll see distance and aperture combo for the automodes, and different distance/aperture combos for manual mode. That's how 99% of the auto flashes I've seen work. Pretty basic but useful. If you want fill flash I recommend dante stellas excellent article fill flash for amnesiacs

You can override the automodes and gain full manual control by exchanging the fotodiode for a potentiometer. Makes the flash even more useful as an off-camera flash. Requires soldering and basic electronic knowledge though.