Final drive oil change

[Grumpy Goat]

Hello everyone,

I just completed the oil change in my final drive and noticed after measuring the old oil there was only 150ml. I drained the oil with the bike on my lift table while on the center stand. I am wondering if the missing 30ml somehow stayed behind in the housing? Has anyone noticed this after an oil change? I should have used my compressor to inject air in the top to push all the oil out the drain
TIA

PS 
There was 180ml of oil in the last oil change and I have no leaks

I have never measured the oil coming out, and I always do it while on the centre stand. 

Satisfied that there was no leaking or sweating of oil I assumed it was conserved and was happy with that. I always put in 180 ml so I know what was / is going in. There will always be some "apparent loss" due to oil staying and coating the innards. This loss decreases in time as the oil is allowed to drain.

Who filled it last time? How long did you give it to drain?