GetSecs returns the time in seconds (with high precision). GetSecs uses
the highest precision realtime clock on each operating system. The zero
point (point in time where GetSecs would report a value of zero) is
operating system dependent and nothing to be relied on.

TIMING ADVICE: The first time you access any MEX function or M file,
Matlab takes several hundred milliseconds to load it from disk.
Allocating a variable takes time too. Usually you’ll want to omit
those delays from your timing measurements by making sure all the
functions you use are loaded and that all the variables you use are
allocated, before you start timing. MEX files stay loaded until you
flush the MEX files (e.g. by changing directory or calling CLEAR
MEX). M files and variables stay in memory until you clear them.

Win : ___________________________________________________________________

On Windows machines the high precision QueryPerformanceCounter() call
is used to get the number of seconds since system start up, if a
performance counter is available. Otherwise, or if the high precision timer
is found to be defective or unreliable, the less accurate timeGetTime()
system call is used. Some windows systems and pc’s are known to have
defective or unreliable timing facilities under some conditions.
Psychtoolbox tries to detect and handle such systems at runtime - it
performs runtime consistency checks. For a more thorough test, run
GetSecsTest. See also the FAQ section of the Psychtoolbox Wiki for more
background info, as well as “help GetSecsTest”. Resolution of time on
Windows varies: If the high precision clock is used, it will be
microsecond resolution and accuracy, if the fallback clock is used, it
will be roughly millisecond resolution and accuracy.

OSX : ___________________________________________________________________

On machines running Apples OSX, the mach_absolutetime() call is used,
which provides at least microsecond accuracy and resolution. To our
current knowledge, all Macintosh computers have reliably working clocks.

LINUX : _________________________________________________________________

On Linux, the gettimeofday() system call is used, which usually has
microsecond resolution and accuracy. Linux always chooses the highest
precision clock on a system for that call, usually the processors
performance counter or the HPET high precision event timer, or the ACPI
power management timer - whatever is the best tradeoff between
reliability, acccuracy and performance. To our current knowledge, all
computers running a Linux 2.6 kernel have reliably working clocks.

See also: WaitSecs, GetSecsTest,