All our notes have different lengths (7mm between denominations) and a lot of equipment relies on a combination of length sensors and optical sensors that check specifically for problems with the notes' transparent windows. The windows are one of the hardest things for forgers to get right and light diffusion checks are a very easy way of weeding out fakes. There is new technology out there that does an optical scan check but our notes are so hard to forge that those functions are mostly used for fitness checks to cull worn notes. They're designed with an international market in mind so they're calibrated by just running a heap of legit notes through the machine and allowing it to "learn" the correct features and dimensions from what it sees. If you're in Oz, you'd program the $20s denomination by running Australian $20s through the machine, but if you're in New Zealand you'd run New Zealand $20s through it instead. Manufacturers have to design their equipment to be flexible otherwise they can't compete effectively so there aren't many "Australia Only" note acceptors out there. A lot of machines out there (like ATMs) are "dumb" and simply spit out X number of items from Y canister because they assume that the human who maintains them knows what is meant to be dispensed (that's why you occasionally hear stories of ATMs that give out $200 when the user requested $80 - some idiot put the $50s in the $20s canister). There will obviously be a fair amount of checking involved and some equipment will need to be recalibrated but it won't be a major issue.