98.6°F is an over-precise conversion of 37°C. The number was originally measured as 37°C, with two digits of precision. It shouldn't have been reported as 98.6°F, though a correct rounding would have been even less accurate: the number is closer to 98.2°F/36.8°C, but the proper rounding of the conversion would have rounded up to 99°F.
There is, of course, significant variation from person to person, so two digits of precision is probably all that's really appropriate.
There is, of course, significant variation from person to person, so two digits of precision is probably all that's really appropriate.