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Like most couples, Daniel Reeves and Bethany Soule fight. Unlike most, they solve their spats with dollars.

When a chore comes up neither wants to do, they put their hands behind their back and think of how much they'd pay the other to do it. Then, at the same time, they show that number on their fingers.

It might be $20 to put the kids to bed, $4 to go fetch tacos in the rain, or $400 to make travel plans. Whoever has the lowest bid does the job and gets paid their bid to do it.

It's basic game theory and behavioral economics, just applied to a marriage.

Folks like Danny and Bethany, part of the burgeoning "quantified self" movement, use smartphones and gadgets to track their goals. From the steps they take, number of emails they answer, and hours they play with their kids, they believe a better you is just a data point away.

For this Portland, Ore., couple, just as in love as when they met nine years ago, their objective is total fairness and zero resentment, using cold hard cash.

"'But I did the dishes last time!' turns into, 'But I did the dishes last time and I got paid $40 for it, so that was kind of awesome!'" said Bethany, 32, who co-founded and runs a startup called Beeminder with her husband, Danny, 38. They have two kids, Faire and Cantor, ages 6.7 and 4.997, according to a program Danny wrote.

If that sounds geeky, that's just for starters.

At one point, they paid each other $24 an hour to watch the kids. At another, Danny paid Bethany about $30,000 in various costs to have their first child while he worked a full-time tech job and she took time off school. Split over what to name their kid, they submitted sealed bids worth several thousand dollars.

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"If the money makes the other person feel valued ─ and like there's a payoff ─ great," said Paula Szuchman, co-author of Spousonomics, in an email. "For some couples a thank you and hug might suffice. For this couple they need something more tangible."

"You need to really appreciate that money is utility, you have to trust in the math so much."

In the couple's ledger, Bethany's balance is -$80,421.10, largely money she owes Danny from grad school. Sometimes she pays for more things out of pocket in "the real world" to bring down her debt in the private books. The plan is their startup's eventual success will wipe out the balances.

"Sometimes it will feel unfair in the short term, but you have to trust that it will be fair in the long term," said Danny.

They do use some tricks to make it easier, like separate bank accounts. To cut down on bookkeeping they also say a random number between one and 10 when they haggle. The chore still gets done, but only if their two numbers match is there a payout, which they multiply by 10 to make up for only one in 10 bids matching.

"Normal people have perfect good approximations of this," said Danny. "This is just nerd level turned up to 11."

For two people who met online and share advanced degrees in computer science, it's a great system.

"You need to really appreciate that money is utility," said Bethany, a concept the couple borrowed from economic theory. "You have to trust in the math so much."

So what about sex?

There's no bartering in the bedroom, they say.

"I don't think we've ever disagreed," said Bethany, because there's never been a time when only one of them was in the mood.

Family therapist Terrence Real has no problem with the cash component. "They use it as a gauge to ask the critical question... 'what's it to ya?'" he said.

However, there can be dangers if kids are involved. "If I was their child and I learned that they were bidding over the task of putting me to sleep I might get upset," said Real.

Daniel Reeves reads his children Cantor Soule-Reeves (rt) and Faire Soule-Reeves (lt) a bed time story at their home in Portland, OR. Leah Nash / for NBC News

Another wrinkle is that the couple hasn't factored for how Danny didn't give birth to two children. He's also earned more in his life, giving him a bigger pot to bet with. They're mulling over whether to give Bethany a lump-sum payment to fix the imbalance.

It sounds mercenary, even cruel. But there are ways within the system to show affection.

Recently Danny and Bethany haggled to see if he would drive her home after a long day of work or if she would have to ride her bike. She bet $15, and he intentionally "lost," so that he could do her the favor.

Communicating in a series of brief instant messages, she replied back with a smiley face emoticon, a symbol of 21st century love distilled down to two characters.

In this blog post, Bethany describes how their system works in more detail. Danny and Bethany's startup, Beeminder, can be found here.