Similarly, the same Display can be reused in
several Watch Models: for example, X334 is used in both Ace and Delicia. The
Buttons and Icons used in Displays are each de?¬?ned only once, and reused in each
Display that has them.
At the middle level, each reference to a lower-levelWatch Application is clearly a
case of reuse. Since the name of a State in the middle-level diagram is the same as the
name of theWatch Application it decomposes to, a State for a givenWatch Application
would be essentially identical between different Logical Watches. We thus reuse the
whole Stopwatch State from the TASTWLogicalWatch in the TASTand TST Logical
Watches. Any improvements to the Stopwatch will thus instantly be a part of allWatch
Models that use these Logical Watches.
At the bottom level, the Buttons and Icons are reused from their de?¬?nitions at the
Family level. The global pseudovariables such as sysTime are also de?¬?ned only once
and reused in manyWatch Applications. This is in contrast with the trueVariables and
the Alarms, which are de?¬?ned local to a givenWatch Application. They may be reused
within that one application, for instance ?¬?rst in a calculation that sets the value, and
later in a calculation that reads the value.
Looking at the Watch Applications, both Timer and Stopwatch contain a
variable called stopTime, but these refer to different things: a Timer??™s stopTime is
the time of day when its alarm will ring, whereas a Stopwatch??™s stopTime is the
amount of time that had elapsed when the stopwatch was stopped.
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