On: Librarian builds self-checkout machine. Costs $150...

[bensummers]

If he had stuff he was doing, then someone else had to do it, and therefore there was a cost. Even if this cost was someone going unpaid overtime.

If he is employed to do such work, then his salary should definitely be counted!

[fefzero → bensummers]

Yes, but then you'd probably have to subtract the amount of time that he would have spent implementing the other type of solution or getting training on how to administer it. The salary doesn't necessarily have to be included; it's a fixed cost.

[ks → fefzero]

We can also assume that his job in technical support did not use 100% of his time. So some of the costs were already there to begin with.