I've been getting on well with this puzzle and have relished the challenge as always. My internal (within the perimeter) answers are all working as expected (so if I get some digits for an Across clue from working out the Down clues, then finally working out the partially-filled out Across clue gives me the expected value. E.g. I got 25dn and 20dn, and then the 1st and 3rd digit of 25Ac correspond with my calculated answer.
HOWEVER.....
My perimeter answers are gobbledegook. I'm assuming that if an error is 5 (so lets say the left hand side of the equals sign is 344 and the right hand side is 349, then my error value is 5) then the letter to put in the perimeter for that clue would be E.
Is that right? Anyone else get gobbledegook?