Upon written request from a consumer of electrical energy, that consumer’s electric meter may be tested. The first test will be at no charge. For subsequent tests of the electric meter, there shall be a fee of $20 for checking a residential meter and a fee of $50 for checking all other types of electric meters. If the meter is not within a plus or minus 2% of being correct, there will be no charge for the test. If the meter is incorrect more than plus or minus 2%, a percentage adjustment will be made for the last 30-day billing period received by the consumer in direct proportion to the percentage that the meter is incorrect.