This is another one of Gossen's many meters with "Six" worked into the name, and it doesn't help matter that they liked this case and used it in other meters with almost identical names. Compare this with my Sixtry, for instance. It's pretty much the same meter.

This appears to be the first of the line. You roll up the corrugated, protective door to expose the face. If you leave the door where it still covers the sensor, it acts as an incident meter. If you roll the door all the way back and expose the cell, it's a reflector.

Learning to use it takes some doing. You have to set the film speed on the knob on the right-hand side. The knob is connected to internal electronics (i.e. a variable resistor) which changes scales. So you point the meter and rotate the knob until the needle moves off zero, and you read the speed/aperture combination it points to. The scales change in whole ƒ-stop increments, so you can flip around and direct-read a combination that you like, or you can read horizontally to see different pairs. It works either way.

A big problem with this is that the needle is short and isn't as easy to read as one might like. Later versions of this meter tried various gimmicks to address it, but ultimately they abanoned it in favor of match-needles and dial calculators like everyone else.