I read a while ago about removing the 'o' ring at the top of the dip stick and so decided to give it a go. The idea is that the 'o' ring creates a good seal and so pushes the oil out of the dip stick tube thus giving a false reading. So today I took a reading and the oil seemed to just be touching the minimum. I took the 'o' ring off and suddenly the oil was just over maximum !!!
So I have drained some oil, taken 3 more reading to check I am in the middle of the min and max. Interestingly, putting the 'o' ring back on gave me barely a drop of oil on the dip stick.
Duratec Dipstick picture from Caterham website.
The 'o' ring is on the yellow plastic section at the top.