Assistance
In the main battery, there was nothing to do besides calibrate the Normandy's guns. Garrus knew and heard the gossip that traveled the ship about him doing those 'damned calibrations. What else would he do? Keeping the guns maintained was something he could do, in order to take things off his mind.
At one moment, Legion – the geth friend Shepard found on the dreadnought – tried to assist Garrus with his calibrations. The geth indicated the guns accuracy could only be improved by .32%. Of course Garrus knew better than that and upped the accuracy by .43%. Legion was legitimately confused.
Garrus couldn't help but smile at this. Proving a synthetic wrong had its benefits.