Maybe it was out of juice, or perhaps he couldn't find the charger, but, for some reason, the timer on Ian Macdonald's iPad was not working on Tuesday.

Which might explain why Gillian Triggs, the Human Rights Commission president and familiar fixture on the witness list of Parliament's estimates hearings, gave evidence for nearly six hours beyond her allocated time.

Things were very different last Friday when Senator Macdonald set his iPad timer to loudly ring every 15 minutes while Solictor-General Justin Gleeson was trying to give evidence over a feud with Attorney-General George Brandis.

In this, as in all things, his wingman, Barry O'Sullivan, had his back.