40 CFR §1065.290

1. (a)Application. Use a balance to weigh net PM on a sample medium for laboratory testing.
2. (b)Component requirements. We recommend that you use a balance that meets the specifications in Table 1 of § 1065.205. Note that your balance-based system must meet the linearity verification in § 1065.307. If the balance uses internal calibration weights for routine spanning and the weights do not meet the specifications in § 1065.790, the weights must be verified independently with external calibration weights meeting the requirements of § 1065.790. While you may also use an inertial balance to measure PM, as described in § 1065.295, use a reference procedure based on a gravimetric balance for comparison with any proposed alternate measurement procedure under § 1065.10.
3. (c)Pan design. We recommend that you use a balance pan designed to minimize corner loading of the balance, as follows:
   1. (1)Use a pan that centers the PM sample media (such as a filter) on the weighing pan. For example, use a pan in the shape of a cross that has upswept tips that center the PM sample media on the pan.
   2. (2)Use a pan that positions the PM sample as low as possible.
4. (d)Balance configuration. Configure the balance for optimum settling time and stability at your location.