NavList:

I have a time convention question with two follow up questions.

Being able to conveniently, or “properly,” convert a particular zone time to universal time and back again by the use of zone descriptions is a basic skill of the celestial navigator.   A popular convention uses positive and negative numbers for the purpose of identifying zone descriptions; more specifically, the zone descriptions west of Greenwich are most often seen as positive numbers while the eastern zone descriptions are labeled as negative: 

1.  Why do I sometimes see, in print, these zone description expressed using the opposite sign as described above?      [As an example, I seem to recall seeing some GPS devices using signs opposite from the convention.  There have been other times when I’ve seen the zone description sign used that did not match convention.

a. If the zone description sign is dependent upon the context of the discussion, I ask the following question:  What would be an example of a legitimate context in which convention needs to be changed in order to satisfy the context? 

b. Is there ever any good reason why a navigator would necessarily speak of a zone description west of Greenwich as Negative?

Steve OCBC