Markoz wrote on Aug 23^rd, 2020 at 3:12am:

My I understanding of the instructions are that adding the "C" is optional, but adding the "F" is a must: Celsius entries cue I or 2 character between 0-99, optionally suffixed by "C". Valid Fahrenheit entries are 1. 2. or 3 character integers between 0-99 suffixed by “F". because the word "optionally" only occurs in the sentence about Celsius, and not in the sentence about Fahrenheit.

That's correct.  "F" must be entered when using Fahrenheit.  I'm using Celsius.  Yet I get the INVALID ENTRY no matter what.