If you leave your altimeter on
QFE-Dunstable you will probably have an additional margin for error
locally but this is not certain
If you
reset your altimeter to QNH you might be able to relate it to altitudes on the map
- Discuss !!!
You have
got to decide if/when to re-set the altimeter and to what (QFE Dunstable is on your map/hand !!!)
Your
computer might give you height agl if it has a terrain database but beware !!!! Altimeter definitely wont.
So - IGNORE the altimeter (or computer) below (say) 1000ft indicated - or as appropriate for the
region and use
your judgement of height to use for circuit and landing.