Josh Barro, "The Final Word on Mitt Romney's Tax Plan", Bloomberg 10/12/2012:
Rosen also depends on aggressive assumptions about macro-level dynamic effects, where taxes rise not because individual taxpayers report more taxable income but because the economy grows as a whole. In other words, he is depending on rosy — and not necessarily warranted — economic assumptions to make the numbers pencil. [emphasis added]
"To make the numbers pencil"? Economists can certainly make numbers do almost anything, but can they also make numbers crayon, or chalk, or dry-erase marker? And what would it mean if they did?
In the case of the penciling numbers, the process apparently starts with a simple conversion: "to pencil (numbers) out" meaning "to write (numbers) out in pencil (to fill in the blanks in a formula)", i.e. as a rough draft:
At intermission, Kraus ducked out to a pay phone and dialed Omaha. He and Buffett penciled out some numbers for a deal. Buffett said something about going on a trip, and Kraus went back to Beethoven, saying nothing to his wife or the client.
Generally speaking, when trying to pencil out a more profitable break-even point, it's best to focus on your costs.
It is conceivable that your Web site could feature all three levels of access — free, registered, and premium — but if so, be sure to pencil out each element to determine how the costs of providing each compares in terms of lead generation, prospect list building, or customer relations.
The use of pencil as a verb goes back to the 17th century — the OED cites
1610 P. Holland tr. W. Camden Brit. i. 631 Lanthony..the situation of which Abbay Giraldus Cambrensis..shall pensile it out unto you for mee.
1621 T. W. tr. S. Goulart Wise Vieillard 98 Horace in his art of Poetrie doth pensill and picture out an old man in this manner.
1631 J. Weever Anc. Funerall Monuments 372 These words thereupon being most artificially pensild.
1641 J. Johnson Acad. Love 34 A garland of painted flowers, which was so lively pencilled and garnished with proper colours, that the laborious bees imagining it to bee reall [etc.].
1673 E. Hickeringill Gregory 256 Clean Latin style..pencill'd whether by himself or any other linguist.
VERB+out combinations often express progress to completion or exhaustion; in any case, the modern "pencil out" examples carry an implication that the penciled-out values add up appropriately, at least in principle:
Something's bound to go wrong or change even though everything is penciled out in your plan.
Then there's a diathesis change: <X pencils out Y> turns into <Y pencils out>, still with the implication that Y adds up appropriately as a plan:
What do the numbers say? Can you afford that media buy? Crunch the numbers. If the numbers pencil out, then by all means go get the money, but if they don't, then don't.
It is possible they might ask voters to approve increased taxes to cover such a position if the estimates pencil out, but Brenaman said that depends on what they learn at Friday's workshop.
From there, a run-of-the-mill inchoative-to-causative shift gives us "to make the numbers pencil out"
"On one hand, we had to create the pond as an amenity, but build the density to make the numbers pencil out," says Coyle, adding that Astoria already is built out when it comes to housing.
Then the (not) well-known phenomenon of out-ellipsis, and …