An analytical balance (or chemical balance) is a class of balance designed to measure small mass in the sub-milligram range. The measuring pan of an analytical balance (0.1 mg resolution or better) is inside a transparent enclosure with doors so that dust does not collect and so any air currents in the room do not affect the balance's operation. This enclosure is often called a draft shield. The use of a mechanically vented balance safety enclosure, which has uniquely designed acrylic airfoils, allows a smooth turbulence-free airflow that prevents balance fluctuation and the measure of mass down to 1 μg without fluctuations or loss of product. Also, the sample must be at room temperature to prevent natural convection from forming air currents inside the enclosure from causing an error in reading. Single pan mechanical substitution balance is a method of maintaining consistent response throughout the useful capacity of the balance. This is achieved by maintaining a constant load on the balance beam and thus the fulcrum, by subtracting mass on the same side of the beam as which the sample is added.