One rotation = one complete turn of the crank. So yes, every time your left knee goes up, for example.

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As for the marks... although you should wipe off your chain after oiling it***, you will probably get marks if you press your calve on the chainring. I tend to do it when I stop at a red light, or when for some reason I stand with my back turned to the bike.

You'll have less of a mess if you clean your bike every once in a while, oil it lightly (only so much is needed), wipe off the chain afterwards and wait until the next day to ride. I usually wash my road bike every 300-400 km (or after a ride on a very dirty road), after a ride when I feel thankful for cycling, admiring the clean bike gleaming feels even better.

*** And not oil it THAT often, i.e. every 300 km is way enough, and just the chain, not all the cogs, and put the oil on a clean chain as much as you can - don't know if there's been a discussion about cleaning your drivetrain on this forum but I'd guess so. If you don't find one and need to know, feel free to ask!!! - Sorry this message is a bit disorganized!!