Built-in Mathematica Symbol

Refresh

Refresh[expr, opts]
represents an object whose value in a Dynamic should be refreshed at times specified by the options opts.

Refresh[expr, None]
specifies that the value of expr should never automatically be refreshed.

	TrackedSymbols	Automatic	symbols whose changes trigger an update
	UpdateInterval	Infinity	time interval at which to do updates

When Refresh[expr, opts] is evaluated inside a Dynamic, it gives the current value of expr, then specifies criteria for when the Dynamic should be updated.

When one Refresh appears inside another, the innermost Refresh takes precedence.

Refresh[expr] resets automatic updating even if it appears inside Refresh[..., None].

The setting UpdateInterval->t specifies that updating should be done at least every t seconds.

Make a dynamically updating clock: