I've only just come across this thread & have read it with interest. I was born in 1930, so have only ever used Imperial; although towards the end of my working life, metric- or SI- was very much in vogue. I felt sorry for those who started metric at the change over for so much was - & still is, eg mph- in Imperial. Dave TT; yes, acre, they built houses then at 10 to the acre which put it into perspective. JohnF; I always used Btu's, & it was so easy to check out 3Btu's /ft3 to give a good indication of room heat loss. MartinR; afraid you are x60 out with the latitude. 1nm is 1minute of arc, not 1 degree. I nm is approx. 1.15 miles or 1 mile is approx. .9 of a mn. In kms, " gawd knows"!