just got some maufactors plans and the scale seems a bit odd anyideas never seen a scale like this before evan on plans from the 60s

Is the rule up the side marked in 1:1 metres?

not too sure but my dad suggested that if i mesure that craft length on the drawing this came to 160mm divide this by the actual legth of the craft it gave me 76 so is the scale 1/76

If the assumed metre marks measure at about 13.2mm, then the plan is about 1:76, a good match for 00 scale railway.