Why must the bulb of the thermometer be opposite the sidearm?

The bulb of the thermometer must be opposite the sidearm to ensure accurate temperature readings. This design allows the liquid inside the thermometer to expand and contract freely in response to the temperature changes in the environment being measured, without interference from the sidearm. By positioning the bulb away from the sidearm, it prevents heat loss or gain from the surrounding environment, thus providing a more precise measurement.