as you say you need to turn it down to 60 i assume the water is too hot, to decrease turn the screw slot anti clockwise, don't why there are no indicators on the stat but you will then need to check temp at tap with a thermometer
Is there a thermometer strapped around you?
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AFAIK, all the ones without numbers on have a series of marking, one of which is longer than the rest. If the marks are completely absent, or are all the same, then you could measure the temperature that comes out of the taps and allow something arbitrary for heat losses through the distribution pipework.
If you're worried about it then install a thermostat that has numbers on it. They are very cheap.
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