Michael just gave a nice summary of what can be happening. Part of the magic of using the directions is that it is normally well within the range of VC paper to adapt.
As to exposure the best book for me was by far, Dunn and Wakefield, Exposure Manual. It is out of print but typically available used. 3rd edition is what I have and is fine, printed as incident meters were becoming modern, 4th edition would be a bit more up to date in that sense but the concepts taught aren't different, either will be good.