The Mac driver can generate scroll wheel events with values which are not integral
multiples of WHEEL_DELTA.  Apps should handle that by scrolling a corresponding
non-integral multiple of what they'd do for a WHEEL_DELTA-valued scroll or, if
they can't, then at least accumulate scroll distance until its magnitude exceeds
WHEEL_DELTA and do a "chunky" scroll.  However, many apps don't do that properly.
They may scroll way too far/fast or even in the opposite direction.

If the registry setting UsePreciseScrolling is set to "n", the Mac driver will do
that accumulation and chunking itself to work around such broken app behavior.