How-to video: slush ice thermometer calibration for pocket digital and dial thermometers.
As a general rule, temperature measurement devices should be regularly calibrated in order to prove their accuracy. Comark has a number of pocket digital and pocket dial thermometers that can be calibrated to ensure accurate temperature readings. The goal of the calibration is to verify that the display reading you're getting is an accurate one.
First, you'll need a suitable container at 250 mL, or 8 oz. container like this one would be ideal. Next, you'll need to crush enough ice to fill the container. Don't be tempted to use uncrushed ice like standard ice cubes. Once the container is full, pour in cold water until the surface starts to turn from ice white to slightly gray in color. The ice on the surface should show just a small amount of water, and not an excessive amount. So, push down firmly on the ice, and pour off any excess. Essentially, the ice should still be allowed to float. Your ice point is now ready for use, and can be topped off as necessary. Depending on how long its needed, simply add more ice, but remember to drain any excess water.
To start the calibration check, simply immerse the probe of your thermometer into the solution so that it's at least 2.5 cm or 1" below the level of the water in the crushed ice solution. You should not allow the probe tip to rest on the bottom of the sides of the container. Now you need to wait for the reading on your thermometer to become stable. We would normally expect a reading to show that is within 1 degree of zero degree Celsius or within 2 degrees of 32 degrees Fahrenheit. To begin calibrating your pocket digital thermometer, press and hold the kal button for 8 seconds. On devices that don't have a kal button, the DH or data hold button is usually used instead. The digital display should show the kal message for around 2 seconds, after which the re-calibration to zero degrees Celsius or 32 degrees Fahrenheit will have been completed.
To begin the calibration on pocket dial thermometers that have an integrated calibration dial, simply immerse the probe to the depth marker and then manually adjust the calibration until the pointer on the dial reads 0 degrees Celsius or 32 degrees Fahrenheit. Remove your thermometer from the crushed ice solution and continue to take measurements as normal.
It should be noted that kal will be displayed on pocket digital thermometers anytime the kal or DH button is pressed for 8 seconds. The thermometer will not be re-calibrated unless the probe is inserted into a crushed ice solution or water bath at 0 degrees Celsius or 32 degrees Fahrenheit.
Watch this video to learn how to re-calibrate your Comark thermometer using crushed ice!