GetSecsTestOS9

Psychtoolbox › PsychTests

GetSecsTest adjusts the time-advancement rate of GetSecs to match
that of GetTicks, i.e. the standard Macintosh 60.15 Hz tick counter.
The Apple-default rate for GetSecs is generally accurate to about
10^-2. GetTicks, which is the time base for the time of day, seems
to be accurate to within a few minutes a month, ie 10^-4.
GetSecsTest adjusts the multiplier in the VideoToolbox Seconds.c to
match the two rates to within 10^-4. You could time more ticks to
achieve a better match, but I don't think the absolute accuracy of
the tick counter warrants matching any more closely. Note that the
SecondsMultiplier value is specific to the machine it was measured
on.

If it is important to your application to have time advance at the
same rate every time you run Matlab, then you may wish to compute
this SecondsMultiplier only once, and to create a script that loads
that specific value into the Screen Preference SecondsMultiplier,
and to run that script at the beginning of every session. Note that
this multiplier has no effect on the internal counter; it merely
affects the conversion of the count to a time.

Screen Preference SecondsMultiplier stores the new value in the
PsychTable, which persists until you quit Matlab. (It's not affected
by Matlab'S CLEAR.)

See Apple's "Technical Q&A HW31 - UpTime's values are consistently slow?"
web http://developer.apple.com/qa/hw/hw31.html

See TimingTest.