There's a Word document (i.e. do the calcs yourself)
here that will fit an A5 kneeboard.
Alternatively, Bob Cox's Excel based
PLOG v7 is pretty good; search in these forums to find details of how to get a copy.
I use
NavBox ProPlan these days myself, but you have to pay for that! It does so much more than just a plog, though, so isn't filed under 'basic'.