There's a sort of urban legend among people I've spoken to about Sinclair that the Executive calculator can't divide by 0. Specifically, if you do this then it goes into a busy loop, cannot be used, and drains/overheats the batteries until they run out or explode. There is an attested story of the cells overheating due to the calculator being left on, but I can't find any evidence that it would become unusable as a result of dividing by zero.

What I can find is that the manual for mine, which is the earlier model with the K switch (serial 19216), describes various overflow conditions and that when they occur, you clear the calculator and start again. I can't test this as I don't have the correct cells to use it.

Also this description of the TMS1802 says that pin 13/D11 is used for overflow and error signalling, which implies that overflow detection is part of the chip. So even if it didn't have /0 protection, it would be able to signal the error and let the user clear/restart.

So is there any truth to the rumour that you could render a Sinclair Executive unusable by dividing by zero? Was there a different electronic calculator that did exhibit that sort of behaviour? I know that mechanical calculators can get into infinite loops when trying that.

  • 3
    I"m pretty sure they handled that case all right by testing the divider. Commented Sep 17, 2021 at 19:25
  • 1
    That would be a fatal flaw in the chip.
    – vonbrand
    Commented Sep 17, 2021 at 22:21
  • Are the correct cells unobtainable these days?
    – dave
    Commented Sep 18, 2021 at 0:04
  • A current limited lab power supply could stand in here.... Commented Sep 18, 2021 at 12:47
  • @Jean-FrançoisFabre this was before the days when a firmware defect that made it into production could be easily mended once discovered. Commented Sep 18, 2021 at 12:48

1 Answer 1


Answer: no it can't. This is a later model Executive with the H/L switch (serial number 131131); apparently my manual and calculator don't match! Anyway, the calculator goes into a loop. It doesn't "break" in that it can be cleared (or switched off, or the batteries removed) but it certainly tries to calculate the answer without detecting an overflow.

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