Not measuring, pinching!
The lad on the left has been given Picquet Duty, but being a strapping country fella, he thought the Boss meant Picket duty, so he is propping up the fence! This is a tedious job, and he has actually fallen asleep on his feet, a skill acquired by many a digger, along with an expression that feigns wakefulness and will fool any junior Lt.
Unfortunately, it doesn't fool his mates, and one has snuck up behind him to steal his paybook and wallet.