AYER — Determining the town’s tax rate for fiscal year 2008 is like trying to pay a restaurant bill by collecting a portion of the total from everyone at the table.

It’s a process the town typically completes by late November or early December, in time for the January tax bills.

The town’s tax collector uses the property tax rate to bill taxpayers for the cost of running the town.

For FY07, the town’s residential taxpayers paid $9.54 per thousand dollars of property value. Its commercial, industrial and personal (CIP) property taxpayers paid $24.10.

The Massachusetts Department of Revenue (DOR) certified Ayer’s property values Nov. 14 after auditing the Board of Assessors’ work during the summer and early fall, said Assessor Tom Hogan. The DOR’s certification process, following the town’s property revaluation, occurs every three years.

“The reason for the revaluation every three years is to keep our assessed values current,” said Hogan. “We review property sales and the market every year though, so we know what our properties are worth on an annual basis.”

The assessors don’t raise or lower taxes, he said.

“We look for the fair market value only,” he said.

DOR certification means the Board of Selectmen will hold at least one public hearing on the tax rate classification before setting the new rate. With the town’s split rate, taxpayers could inform the selectmen that they prefer a higher residential rate and lower CIP rate in the interest of attracting more business to town.

The cost of local government, set at town meeting each year, is like a restaurant bill, said Hogan, and the taxpayers are like the diners. The assessors are like the diner who takes charge and says, “OK, who had the filet mignon?”

The assessors’ task is to make certain each taxpayer’s bill for his or her share of Ayer’s costs is equitable.

Simply dividing the total bill by the number of diners would mean the diner who ate the hamburger would overpay, and the diner who ate the filet mignon would underpay.

The assessors’ task is to see that that kind of in-equitability doesn’t hold true for Ayer’s taxpayers, said Hogan.

“We want to make sure each taxpayers’ burden is equitable,” he said. “It’s based on the value of the taxpayers’ properties. We list and value all the properties in town at 100 percent of their fair market value. We refer to the properties’ values as their full and fair cash value. That includes residential, commercial, industrial and personal properties, such as cars.”

Ayer’s current residential rate is less than the average residential rate of $10.26 for the nine towns under the Nashoba Valley Chamber of Commerce.

Since 1997, its residential rate has varied between a low of $9.07 in 1997 and a high of $11.32 in 2000. Its average between 1998 and 2007 is $10.09.

However, its CIP rate of $24.10 is nearly twice the average of $12.79.

Ayer’s CIP was lowest in 1997 at $18.63. From 1998 to 2007, its average has been $21.93.

Ayer’s 2007 residential rate is also less than the average commonwealth residential rate of $10.41, but its CIP rate is substantially larger than the commonwealth’s, which is $13.13.

Since its CIP rate is comparatively larger, Hogan said the town could appear less attractive to business investors interested in the region.