[tz] Official definition and origin of the term "Central European Time"

[Paul Eggert]

On 10/23/2015 01:52 PM, Even Scharning wrote:
> All credible sources I have found, say that CET is a constant UTC+1.

Many sources also use "Central European Time" to denote either UTC+1 or 
UTC+2, depending on whether daylight saving time is in use. For example, 
"Most of the cities in this book are on Central European Time, which is 
1hr. ahead of Greenwich Mean Time (GMT) and observes Daylight Saving 
Time during the summer." -- Let's Go Europe 2012.

North American practice is to use phrases like "Pacific Time" when one 
wants the time zone independently of whether DST is in use, and phrases 
like "Pacific Standard Time" and "Pacific Daylight Time" when one wants 
to specify whether DST is in use. There's no similar convention for 
European time zones, so phrases like "Central European Time" are 
ambiguous in practice, and careful writers should specify which meaning 
is intended -- as is done in the abovementioned quote from "Let's Go 
Europe".