Minnesota’s U.S. Senate recount is so refined, so elegant, so perfect that even its greatest excess — the unbridled, tit-for-tat ballot-challenges by both the Al Franken and Norm Coleman campaigns — has been raised to an art form. Monday’s recount action may have been replete with the apparent messiness of lost-and-found ballots and the seeming ugliness of surly officials sending challengers into tears, but it ended on a grace note of pure, mathematical-political-electoral beauty.

With more than 2 million ballots having been recounted (three-quarters of the 2.9 million that were cast on Nov. 4), the ballots that the Franken and Coleman camps have challenged are as near to being equal in number as near-equal can be: Coleman, 1,401; Franken 1,400.

As the ballot challengers work in harmony with the music of the spheres, the unchallenged ballots continued playing the same dirge on Monday that we’ve heard for weeks now: there’s an advantage for Coleman in the low three-digits. Today the gap between Coleman and Franken is 172, according to figures from Minnesota Secretary of State Mark Ritchie’s office.

In an election that the State Canvassing Board found was within 215 votes (in incumbent U.S. Sen. Coleman’s favor) after the initial canvass, the rival camps are now running virtually neck-and-neck in the amount of challenged ballots: Coleman has challenged 948; Franken, 945. The challenged ballots aren’t counted in the final total until the Canvassing Board reviews them.

Meanwhile, the margin between the candidates continued to hover between 100 and 200 votes, standing at 167 (with Coleman still in the lead) as of 8 p.m. Saturday — when the office of Minnesota Secretary of State Mark Ritchie released its official figures for the day. (The Star Tribune keeps a different set of numbers based on its own information gathered before and after 8 p.m. at recount sites across the state.)

It’s so close that Democrats have asked voters overseas to call their local election offices in Minnesota to find out if their absentee ballots were rejected — and if they were, to relay that to the party immediately. The State Canvassing Board meets Wednesday to discuss the question of counting improperly rejected absentee ballots.

(Minnesota Secretary of State Mark Ritchie predicts 1,500 challenged ballots, and fivethirtyeight.com’s Nate Silver estimates roughly 1,800. But since every campaign challenger at every recount site represents an independent variable, I think my guess is as good as theirs.)

More complicated math, working with the rate of increase rather than the hard-number jump, suggests the combined total could hit 2,518. That’s if each campaign were to continue to become increasingly picky over the next two days — at the same percentage rate of increase they showed from Day One to Day Two.

For Franken, the day-over-day increase so far is 42 percent, which if repeated on Day Three and Day Four of a projected four-day recount, would lead to a total of 1,233 challenges.

For Coleman, who had a 44 percent increase from Day One to Day Two, the grand total would be 1,285 challenged ballots, if he were to keep increasing his challenged ballots by 44 percent each day. Drilling down, that means he would challenge 373 on Day Three. And on Day Four, Coleman’s daily challenged ballot count would be – hold on to your hat, Nate Silver! – 538.