The nautical mile is roughly equivalent to a minute of arc along any meridian and is the same at the poles as the equator. It's the geographical mile that's measured along the equator.

The British nautical mile is of course something completely different and somewhat longer than the statute mile which is based on I know not what. 

Kato will no doubt be along in a while to fill you in on all the detail.

John the pedantic geologist.

Its about 92 chains, and its something to do with a length of sea of the coast in southern england.

In SI units its about 1.25 Metres longer than a nautical mile.

Invented to enable british to destroy johny forigner navys as we would always be closer to them then them to us.

XCman, is that 92 chains as you buy them from the shop, or after you have taken 4 or 5 links out to make it the correct length?

Do we need to make a further correction then for a Powerlink?

Ive got a question, Ive got a garmin Edge, and when your on the trial I stopped to 'Mark The location' I checked this with our OS Map and the refence the 'Edge' gives you is completely diffrent. Why doesnt the Edge give you OS ref i.e(st125413)???

I dont think it does, I only think it does the GPS location???  does anyone know??