Many manometers require calibration, and this may be carried out by the (1) static method in which simultaneous readings of the manometer under test and the primary standard are taken when one limb of the manometer and the standard are connected to a variable pressure source, the other limbs being connected to a source of constant pressure, or (2) the dynamic method in which the difference in pressure obtained between a low-speed atmospheric wind-tunnel hole (static pressure) and the atmospheric static pressure is used to carry out the calibration. One limb of the manometer and the low-pressure side of the Chattock-Fry are connected to the tunnel-wall hole (reference variable pressure), while the other limb of the manometer is connected to the atmospheric outlet of the Chattock-Fry.