Front side, from top to bottom: old WataCombiMeter, newer WataCombiMeter, newer WataMeter (Super), older WataMeter (Super) and Präzisa rangefinder for comparison.
Back (eyepiece) side.
Seen from above.
There are 3 versions of the WataMeter: I, II and Super. The I is an ordinary rangefinder, you make the two images coincide via turning the wheel and read the result from the wheel. The II has a scale well visible inside the rangefinder, no need to look at small numbers on a wheel. So it has no numbering on the wheel. This is what the inside scale looks like:
The distance set between 3 and 4 meters.
The WataMeter Super has the features of the II pus a scale on the wheel for close-ups between 30 and 50 cm (12 to 20"). It works very well, but going this close creates a problem: The camera distance setting in the old days was calculated from the last element of the lens, the meter calculates it from its mirror, that is the middle of its housing. So you have to measure the distance between the lens of your camera and the meter installed once and then always subtract this value from your measured result.
WataMeters can easily be calibrated horizontally, there is a screw in the middle of the wheel. If the images do not coincide vertically, this doesn't influence the result, but you might not want it nevertheless. There is a small wheel on the left side (seen from above) of the housing of the newer models, on the older ones it's a screw hidden under the leathering.
The WataCombiMeter is an ordinary rangefinder like the model I with addition of an extiction light meter in a very simple version, visible in the second eyepiece. It only works between 17 and 23 DIN or 40 to 160 ISO (17 to 21 on the old one). Extinction meters are more a guess than measuring. This is what you see:
You have to direct the meter towards your subject and look into the second eyepiece from a distance between 20 - 30 cm. There are numbers from 3 to 7. You take the lowest number you can see, it's the 4 on the photo. On the scale at the top there are three scenes, indoor, cloudy and sunny with 3 DIN/ISO settings each. Put the according point on the scale on the number you read and it will show you the shutter/aperture combinations. As I said, it's a guess, but maybe better than nothing.
The instruction notice in English, German and French is here and in Spanish, Portuguese and Italian it's here, the image will open in a new window.
If you buy a rangefinder, check, whether the mirrors are fine. I have a lot of dead rangefinders, like the Präzisa on the picture. It's better to buy from a professional or even better to check with your eyes.