Oil question, 52 plate mini cooper S, help a newbie!

Hi all,

Ive recently bought a Mini Cooper S which i absoluely LOVE!!! However, I have a problem, which may be really really stupid, but i just cant figure it out... I need to top up my oil in Mya (my mini) however, i cant tell how much oil is actually in there?? The dip stick has a yellow "blob" on the end and has been dyed by the oil over the years.. i cant tell how much oil is in there and i dont know how much oil ive put in? i dont want to over fill her, so each week i have been putting in oil gradually..

Please can anyone help??

thank you, Lisa x