I always end up with a 10m square. how do I chose a larger, say, 100m square. If I zoom out the default still seems to be a 10m square. Don't know how the 'hold -' and 'hold +' work.
What are you trying to do with the map, submit a record or view one? I would ignore the hold - and hold + along the bottom of the screen and use the navy bars along the left of the screen to zoom in or out. So if you are submitting a record, start by searching for as nearby place, e.g. Norwich, then use the plus symbol to zoom in, and if you zoom in too much (so you get to a 10m square) just use the - symbol to zoom further out. The further you zoom out the larger the selected square becomes, so it goes from 10m (8 figure reference) to 100m, 1km, 10km.