Trying to scale Eric's files for 50% printing proved a nightmare.
Adobe Acrobat only allows limited scaling. Trial and error with the page options failed.
Searched possible options and found, at last, free download of FoxitReader HERE.
FoxitReader has a %scaling option , just set 'Scaling type' to 'Custom' and Robert is your mother's brother.
Having measured the print it is a little variable - just use a constant value to ensure all prints are compatible!
Also, switch centering off - then you can send the card into the printer the other way round and get two prints on the same A4 sheet. (now 4 would be even better ?)Now there is just the question of cutting and assembling................................(but I will stick with card models ..I am hoping).