Recently on a couple of occasions, we have had test consultants use a "micro" S-type Pitot tube in place of a Standard Pitot tube in stacks less than 12 inches in diameter. After consultation with EPA, it has been decided that without an appropriate calibration in a similarly sized wind tunnel to the stack being tested (reviewed and approved by EMS prior to the test date), the use of a "micro" S-type Pitot is prohibited. Testing in stacks less than 12 inches must use a Standard Pitot tube in accordance with EPA Methods 1A and 2C.