Thanks Peter. I am actually being trained by Tamsin Slatter for a few days. Since my last post I've come a long way, mainly thanks to her.
One other thing you might be able to help me on:
I've drawn/designed a pergola detail which has arcs and rectangular shapes. Took a while. When I came to dimension it, one of the dimensions is different from its what-should-be-identical opposite by 1mm in 430mm.
Do you know if there's some kind of override that disables the interactive nature of the dimension tool, so that I can edit it by that (annoying) 1mm?