Something just occurred to me today. I've puzzled for some time why it is that normal clocks tick slower when in a deeper depth of gravity but that pendulum clocks do the opposite and actually tick faster when in a deeper depth of gravity. Can time tick slower and faster? I believe I now see a fundamental difference between the two clocks. Ordinary clocks with springs, etc. are usually squashed when in a deeper depth of gravity whereas pendulum clocks are actually experiencing stretch because they rely on hanging pendulums. So my generalisation would be that squashed clocks tick slower and stretched clocks tick faster as an observation. Certainly a pendulum clock in free fall won't tick at all. Of course that is not what experimental evidence of planes flying around the Earth and vibrating cesium atoms tell us does it? But none-the-less the difference between the apparent relative time of conventional clocks and pendulum clocks does interest me still. I wonder why the difference is?