I always depended on the amber/yellow oil light to come on when I was 1 litre/quart lower than optimal. It has worked for me for tens of thousands of miles and reminded me to top up when my engine tried to be a hybrid to burn both fuel and oil. I noticed driving with concrete barriers on the shoulder a slight ticking sound like a lifter sound from various other engines. I knew it wasn't like that before then I remembered earlier I was marveling about my new oil change thousands of miles ago about not having to top up every 1,000 miles as I did before since the low oil indicator light never turned on. The car was completely smooth and driving nicely this morning. The silky inline 6 purring and revving freely as a BMW engine should.
So today I decided to check the dipstick after giving her a good detail. I pulled the dipstick out to see it dry. Poooor ZHP...I apologized to her and started to feed oil down her thirsty throat. When the level got to optimum at the top of the highest notch, she drank 3L/quarts of oil.
So remember to check your oil because the oil light may retire at any moment. My car is happy now and is enjoying a 6800 rev without any added friction. Time to change her oil early because of this. I'm glad I have a magnetic drain plug to catch any foreign metallic material.