Wonderful! That site gives tests that can be performed from the keyboard to distinguish between Casio and non-Casio architectures, mentions the invisible 9th di

Wonderful! That site gives tests that can be performed from the keyboard to distinguish between Casio and non-Casio architectures, mentions the invisible 9th digit of precision, and notes that some calculators get it wrong. The old Sinclair pocket calculators had some known arithmetic inaccuracies.