No. The Assessor calculates the total assessed value of all taxable property in Boxborough. The tax rate is simply a mathematical equation that divides the amount approved at Town Meeting to be raised through taxation (called the levy), by the total value of taxable property.
For example, if the total taxable value is $800 million, and the approved levy amount is $10 million, the tax rate would be $12.50 per thousand: 10,000,000 divided by 800,000,000 equals 0.0125 times 1000. If your property is valued at $400,000, your tax bill would be $5,000. If values rise the next year by 20%, the total value for the town would be $960 million. Assuming the same levy amount to be raised, the tax rate would drop to $10.42 ($10 million divided by $960 million times 1000). Your new assessed value would be $480,000 with the 20% increase, and your new tax bill would be $480,000 times 0.01042, or $5,000.