do I feel stupid! many thanks. It takes lots of clicks on my garmin e trex legend but it does do it.I guess this isnt totally accurate or there wouldnt be all that complcated stuff written about it! One thing I did gather (I think) is that as well as changing to British grid, you need to change the map datum to OSBG instead of WGS 84. There is no mention of this is the instructions but it seems to make it more accurate - am I right?
K Senrab