First, the impact of personnel readings
When reading the glass thermometer, if the eye sight is not perpendicular to the glass thermometer, the reading will be higher or lower. For first-class mercury thermometers, through the positive and negative aspects and take the average, to eliminate or reduce the reading bias.
Second, the scale displacement on the value of the show
As the glass thermometer glass after thermal expansion, resulting in internal standard thermometer scale and capillary relative position will produce small changes, thus affecting the temperature indication, a measurement of uncertainty component. In general, this component due to thermal expansion is negligible.