FYI, Glossary for those who are interested; calibration: a scientific term for a standard way of doing something.
eg you can push your bicycle wheel really fast and have it rotate 200 times in a minute, define a minute to be 200 rotation of the same wheel at a pace when you spend a precalibrated amount of force and/or energy, define a minute to be 10 seconds and get a second = 20 rotations of this particluar wheel where every part is accurately designed to produce these wheels and run at a precalibrated energy/force so that the energy/force does not vary from one wheel system to another and is produced by watch company Seiko and you install this wheel on the top of your building. That would be a clock that reads seconds and minutes in a predefined way. A clock is not a time device its an energy device primarily. It calibrates energy input and reads time output. If energy goes wrong time will.
A clock is a device that knows how much energy is input and at what “time” rate. Time-rate can be arbitrary in nature but NOT in a clock. A clock is an anthropic time device. A clock is designed to know what energy is spent for a predefined uniform rate of spending that energy so that, that uniform rate is called time. But time in nature can be understood by studying any energy devices. To understand their uniformity [flatness] and design is called Physics. Every physical device is a clock. We just may not know howto read them.