Under Windows in some timezones (those which do not have Daylight Savings Time,) clock.tcl's [GuessWindowsTimeZone] fails, because it does not expect to find the StandardStart and DaylightStart registry values to be empty.  This results in a fallback to :localtime timezone when the registry has actually supplied all the information necessary to discover the TZ.

Perversely, Windows reports DaylightBias of -60, even though it can never be used.

The observed values reported by Windows are: Bias -420 StandardBias 0 DaylightBias -60 StandardStart "" DaylightStart ""