With the $3.5 billion BART bond measure officially on November's ballot, one might think that the basic facts of the matter — like how much it will cost local homeowners — would be agreed upon details. But not so. The East Bay Times reports that the numbers floated by BART officials detailing annual costs to homeowners may be on the low side — by as much as half.

The paper notes that at a May 26 board meeting BART's assistant general manager for external affairs, Kerry Hamill, told the board and public that, if passed, the bond would cost Bay Area homeowners between $35 and $55 every year for the next 30 years. Instead, the paper reports, the true number is more likely to be closer to $79 annually in Contra Costa, $83 annually in Alameda County, and $111 annually in San Francisco. Oh, and that 30 year thing? The paper says it's actually going to be more like 48 years.

So why the discrepancy? The Times offers one possible reason: Math is hard.

"As for the amount of the tax, Hamill relied on a document [controller-treasurer Rose Poblete] provided showing the estimated average annual levy for an average home in each of the three Bay Area counties," explains the paper. "The complex calculation relies on annual tax rates derived by estimating the bond repayment amount each year and forecasting for the next half century the total assessed value of property in the three counties. Poblete then applied those annual tax rates through 2065 to a home in each county with a current average assessed value."

There's just one, possibly glaring problem: "[She] did not increase the value of that home over time."

We reached out to BART, and spokesperson Taylor Huckaby said that while a more detailed explanation of the discrepancy would be forthcoming, the numbers aren't about to change. "[Yes]," he wrote, "we are absolutely standing by what we have previously said."

The Business Times picked up the story and noted that with a two-thirds majority needed to pass, this news could spell trouble for the currently popular bond measure.

Either way, the difficulty pinning down the exact cost of the bond reminds us of one certain fact: Things at BART need some sorting out.

Related: Despite Spending $2.5M, BART Still Doesn't Know What Caused Mystery Voltage Problem