The 2005 Australian $1 error coin struck 15% off-centre is a remarkable example of a significant minting mishap that escaped the Royal Australian Mint’s rigorous quality control processes. This error occurred when the coin blank (planchet) was not properly seated in the striking chamber, resulting in a visibly misaligned design where approximately 15% of the image is missing, leaving a crescent-shaped blank arc along the edge. Such off-centre errors are rare in modern Australian decimal coinage and are highly sought after by numismatists due to their dramatic visual appeal and the insight they provide into the minting process.