I was playing with a new Mini (not mine), F55 1.5d to be exact and there is no oil dip-stick, instead you have to use the on-board computer to run an oil check, which then displays the results on the centre console screen, similar to this one, but imagine an image of a dipstick with a level indicated on it:
That bit is quite simple, you would think a sensor just detects how much oil there is and displays it on the screen, however, to measure the oil, you have to have the car running and in neutral, which then prompts the system to start checking the oil.
On older engines, I have always waited for the car to cool and the oil to return to the sump to get an accurate measurement of exactly how much oil is in the sump and therefore, available to the engine. My understanding is, if the engine is running or has just been run, the oil will be distributed around the engine, in the journals, head, passageways, turbo etc, so the amount in the actual sump will appear to be lower.
So, how do new engines, without dip-sticks measure oil?