What is the first step in calibrating a thermometer?

The first step in calibrating a thermometer is to fill a cup with ice and water. This method involves creating a reference point that represents the freezing point of water, which is 32 degrees Fahrenheit (0 degrees Celsius). By using a mixture of ice and water, you ensure the thermometer reads accurately at this critical low-temperature point.

To achieve accurate calibration, it's important that the ice used is clean and that enough ice is present to form a solid mixture with the water. This step allows for the thermometer to be set to the correct baseline temperature. Once the thermometer is submerged in this ice water mixture, adjustments can be made to ensure accurate readings.

The other choices involve methods that are either not related to the initial calibration process or do not create a reliable reference point for securing thermometer accuracy. For instance, waiting for one hour does not provide any immediate data for calibrating the thermometer, and placing it in boiling water or warm water would serve to calibrate it at a high-temperature point rather than establishing a foundational low-temperature standard.