The biggest surprise to me is why this wasn&#x27;t caught during testing - especially since testing a relatively simple app like a calculator is often used as an example of how to do testing: try the biggest numbers, smallest numbers, zero, and some values in the middle. There&#x27;s emphasis on testing the extrema, since that&#x27;s where bugs (like this one) are most likely to appear.<p>I should also mention there&#x27;s another suitable replacement, the free Microsoft Calculator Plus:<p><a href="https:&#x2F;&#x2F;www.microsoft.com&#x2F;en-us&#x2F;download&#x2F;details.aspx?id=21622" rel="nofollow">https:&#x2F;&#x2F;www.microsoft.com&#x2F;en-us&#x2F;download&#x2F;details.aspx?id=216...</a><p>It&#x27;s got a horrible early-2000s skin but you can turn that off easily; otherwise it works just like the old one with a few extra features (which I personally don&#x27;t find too useful.) It&#x27;s strange they didn&#x27;t just ship Windows with some variation of that. Ever since I was caught by the modality &quot;feature&quot; (decimal points and trig functions don&#x27;t work in &quot;programmer mode&quot;!?) I&#x27;ve replaced calc.exe with Calculator Plus.