BAXI BOILER TEMP SETTING

[HD840]

My floor standing Baxi boiler for central heating/hot water has a temp setting on front going from 1 to 6...how does this relate to actual temperature (ie. if 6 = 84 degrees then does 5 = 70 and so on).

And instruction on inner door states max setting in Winter....does this not lead to horrendous gas bills, or is this the most economical way of doing and then setting your room stat to required temp.