Lane said she had implored the board, in vain, to send an appraiser to inspect the house. "I cannot understand how you can assess someone's home," she said, "if you haven't been to it."

Back on St. Albans Street, Lisa Parsley was so angry that she, too, protested to the BRT. She armed herself with homemade color-coded charts showing her assessment to be as much as seven times her neighbors'. When she asked the board how it could be so out of line, she said, one member responded: "We have no idea."

In February, without explanation, the BRT lowered Parsley's assessment by 74 percent, from $112,000 to $28,800. However, that is still as much as 50 percent higher than other houses on her street. The board also informed her that the reduction would be in effect only for the current tax year, leaving Parsley further mystified.

Brett Mandel's contempt for the Philadelphia property-tax system makes the news from time to time.

A former assistant city controller, Mandel is head of the tax-activist group Philadelphia Forward. He also owns a home in the 2300 block of Lombard Street in Center City. He bought the three-story rowhouse for $416,000 in 2002, and since then values in the neighborhood have appreciated nicely.

Mandel was well aware that his property was "dramatically underassessed," he said. According to city evaluators, its market value was just $158,000. In August, they raised it to $169,800, nudging up his annual tax bill by $312. Mandel knew he was still getting a big bargain.

He appealed anyway. He argued on the ground of nonuniformity - that assessments on properties of comparable value were not only lower but also higher than his. They are so out of whack across Philadelphia, he has contended, that it's wrong to raise any homeowner's taxes.

The board wound up rolling back Mandel's new assessment - but not everyone else's in the city.

"It's crystal clear that the system needs reform," Mandel said. "There's something broken here."

Simplicity? Not so fast

Even the BRT has wanted to do it - for more than six years.

In 2002, the board announced a two-step master plan to upgrade the agency's computer power and make the property-tax system easier to understand. The overhaul was supposed to take place by 2007. Clearly, it didn't.

The BRT already has spent more than $4 million on new computers and the development of statistical models that accurately analyze market trends. It's a work in progress, as assessors still are learning how to use the new equipment, Mescolotto said.

The second step is far more politically perilous: the conversion of assessments to actual market values, ending the bewilderment of the fractional system.

The "full value" project would make the system fairer. Property owners could figure out more easily whether their assessments were close to reality. Each would pay the correct amount - neither subsidizing neighbors nor being subsidized.

Under full value, all assessments would be revised to 100 percent of market value. In other words, a house worth $100,000 would be assessed at $100,000, not $32,000 or $12,000.

Residential assessments would, on average, be about eight times higher than they are now. In turn, millage would have to be reduced to one-eighth of what it is.

While the city would collect the same amount of money overall, individual taxpayers would notice a difference in their bills - for many, a big one.

According to an Inquirer analysis, 39 percent of property owners would see their taxes increase $100 or more, and 37 percent would get decreases of at least $100. The average increase would be $910, the average decrease $985.

The steepest hikes would hit parts of Center City and South Philadelphia. Neighborhoods enjoying the greatest relief would include Southwest and Northeast Philadelphia.