It is recommended that they should be calibrated every 6 months for theoretical "100% accuracy", however 100% is bullshit for these handhelds, so I compromise and get mine every year... though it's not that often I want (or have the need) to drive after a session and need to be tested...

I don't flip a coin when I'm near the 0.05 mark... c'mon, whatcha expect from,

If your first cut is too short... Take the second cut from the longer end... LBD