New answers tagged metrology
The counting is done by the signal generator. The clock contains a signal generator that generates the 9,192,631,770 Hz signal going to the microwave transmitter. This generator contains a counter that counts every cycle the generator creates (though as The Photon says it may use a prescaler).
Nowadays it's reasonable to make an actual digital counter that operates at 10 GHz. Even so, you might rather use a prescaler to divide this frequency down to 1/4 or 1/8 of the microwave frequency before you actually start counting cycles. In olden times you might have generated your 10 GHz signal by multiplying up a lower frequency (maybe in the 100's of ...
As David has mentioned, you are interpreting too much into the value 101'325 Pa. This is an average pressure which can change quite a lot depending on the weather. E.g. if you are in a low pressure system, the sea level pressure can be far bellow 100'000 Pa, If the local weather is a high pressure system, it will be much higher than 101'325 Pa. Of course ...
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