> For count rates over 5000 c.p.s. it's not so easy. You spend a significant
> part of your time processing counts so the chances of missing one reach
> several percent. For high count rates I would add a 4-bit TTL counter which
> you can read and clear. This allows much higher count rates.

As a rule, I like to avoid resetting counters.  It's usually much better to
let them free-run and "reset" them by keeping track of the old position.  By
doing this, the software may read and [logically] reset the count atomically,
with no risk of missing a poorly-timed count signal.