Reversing Sinclair's amazing 1974 calculator hack - half the ROM of the HP-35

This is great. Scientific calculators usually provide constants such as e and π but there was no space in the ROM for these constants. The Sinclair Scientific used the brilliant solution of printing the constants on the calculator's case

That is so classic Sinclair. Barely working enough to be useful ("three decimal places of accuracy at best", "sin 1 takes about 7.5 seconds", and constants like pi and e are written on the case instead of fitting in ROM), but useful nonetheless, and dirt cheap. Sinclair products were almost comical in how ingeniously their engineers shaved off any pennies they could. In the ZX81, the video circuit is a bizarre and extremely interesting contraption that abuses the Z80's DRAM…