At work I often find myself staring at numbers in Visual Studio’s Watch window. Attempting to compare the sizes of ten digit floating point numbers is error prone in the default variable-width font. The fifteen minutes I spent staring myself blind at a piece of code before realizing that 511111111 is in fact greater than 7682777 was the last straw.
If you use the Visual Studio debugger, I highly recommend switching to a monospaced font in the watch window. Navigate to Tools > Options > Environment> Fonts and Colors > Watch Windows and pick your favorite!