A growing group of West Tisbury taxpayers, furious at their property tax bills and concerned about how the taxes are computed, received little solace during a stormy two-hour informational meeting with Vision Appraisal Technology on Tuesday evening at the Howes House.

The taxpayers remarked later that they are still trying to finding the Rosetta stone, as one put it.

Nearly three dozen West Tisbury residents appeared on Tuesday night, armed with questions for Vision Appraisal spokesman Stephen Ferreira.

Edgartown assessors hosted a similar session on Wednesday night, but with none of the rancor seen in West Tisbury.

Both West Tisbury and Edgartown contract with the Northboro company to develop annual property valuations. Only Chilmark, among Island towns, does not use Vision Appraisal.

On Tuesday night in West Tisbury resident Lawrence H. Schubert raised the question of disproportionate assessment. He said his taxes have increased “very little, perhaps five per cent, but about 100 of my neighbors are facing a train wreck here. I feel they are underwriting my taxes,” he said.

Mr. Ferreira spoke for 30 minutes about the complicated process for developing valuations, which involves an examination of market sales from the previous year and the use of a formula that divides the town into neighborhoods and then applies a variety of factors, called condition factors.

He said Vision Appraisal’s process begins with land appraisal, its zoning use, neighborhood location and finally its location relative to waterfront and water view.

Appraisers then consider the home in relation to size, components (such as number of bathrooms and bedrooms), the quality of construction and the condition of the use relative to similar houses in the neighborhood.

Mr. Schubert said the formula appears to exclude the people factor.

“In my opinion the equation of math and people here does not work, We need to put the people piece back in the equation,” he said, drawing applause.

Following Mr. Ferreira’s explanation of the process, a torrent of questions went on for some 90 minutes.

Assessors were generally silent throughout the proceeding. “This is an informational meeting for you to talk with Vision Appraisal,” said assessor Cynthia Mitchell.

Taxpayer questions ranged from individual property questions, such as wetland valuation, to broader issues about the degree of latitude allowed Vision appraisers and the board of assessors.

Mr. Ferreira said discretionary roles are limited for assessors and for Vision Appraisal, which relies on prior year sales as a benchmark.

One such sale has drawn taxpayer attention this year. A 2006 $19 million sale on the Tisbury Great Pond, more than double the assessed value of the property, has had the effect of doubling and tripling some property tax bills around the Great Pond.

On Tuesday one taxpayer asked which entity — Vision or the town assessors — had included the sale as a full and fair market sale. Mr. Ferreira said the decision was made by the assessors, an answer that drew howls from the audience.

Mr. Ferreira also said the Department of Revenue has developed detailed rules that towns and Vision both must follow. “Unlike the income tax which deals with individuals, appraisals only look at properties, not the individual’s ability or inability to pay the taxes on them. Often there is a disconnect,” he said.

He admitted that the process is subjective, but said it is nonetheless time tested.

“Remember that an assessment is an opinion of value and to that extent is not scientific, it is subjective. But we’ve built a model over 30 years that works,” he said.

But many taxpayers remained unsatisfied at the explanations. Said one in an aside to Mr. Ferreira during the discussion, “We’re behaving well tonight. You’re only feeling the tip of the anger here.”