Senior Plaid Cymru figures and actual figures regarding expenditure and cuts haven't always mixed well at this election.
Plaid's parliamentary leader Elfyn Llwyd took a pasting on Dragon's Eye a few weeks ago. Perhaps the dog had eaten his homework, or perhaps he'd left it on the battle bus. He certainly didn't have the answers at the ready.
By how much and where would Plaid cut in order to save the money needed to pay back the deficit? He talked about Trident and Eurofighter and ID cards saving billions but his line on cuts was vague: "Yes there will have to be some form of cuts at some point" but not now.
Which figures had persuaded Plaid that introducing a maximum wage was a good idea? Could he name a single successful economy where they have a maximum wage? He couldn't. He was quite sure that there was one but as to where ... "in Europe" was as close as it got. No blueprint then asked Felicity Evans? No, said a man willing the interview to come to an end "but why shouldn't we have ambitious plans."
There are those who don't believe that Plaid's figures add up, no matter how you present them.
There are those who have faith in the maths but wish they were presented with more conviction and accuracy.
They will have enjoyed Dr Eurfyl ap Gwilym, Plaid's economic adviser talking to Jeremy Paxman on last night's Newsnight.
Chapter 9, table 9.2 is the one you want. If you're interested it'll tell you many things but one thing it tells you for sure: when he was in school Eurfyl ap Gwilym never left his homework on the bus.