In the age of flat rates, you can talk on the phone until your ears are burning. Yet, back in the 1970's, long-distance calls could easily get really expensive. For one minute, the phone company charged up to 1.26 German Marks, so if you didn't want to pay exorbitant phone bills, you had to keep your conversations short.
A device that provided help with that was the Kienzle "Telestop", a stopwatch with a ten-second scale which was placed conveniently next to the phone so callers could always keep an eye on the time. An additional rotary disc even allowed them to determine the phone rates right away.
The time of the least expensive long-distance calls was between 10 p.m. and 6 a.m., when the significantly lower Moonlight Rate applied. However, only the really lucky ones got a free line at those hours, because the Moonlight Rate was so popular that the phone network reached its limits, and long lines used to form in front of the phone booths.
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