Thanks for the reply.
I would say PT
is the geographic region that switches between PST
and PDT
, while PDT
is a specific offset from UTC
.
In fact, Wolfram|Alpha displays a widget in the results denoting the time offset from GMT
, which is equivalently the winter timezone for the UK. GMT
is not currently in effect there either (currently we're under BST
), so I'm not sure your interpretation would be consistent with that aspect.
As I interpret it, regardless of whether they are geographical, PDT
being defined relative to GMT
means it should always be GMT-7
. Even if we disagree about whether we should even bother calculating in PDT
throughout the year, I would expect Wolfram|Alpha to display an exception rather than something confusing and/or wrong.