# Background Essay: Reading a Thermometer

Many measurement tools can give you a precise measurement, such as a digital scale or a digital thermometer. Other measurement tools have markings at regular intervals that allow you to estimate a measurement by determining the increments that have been marked off.  For example, liquid measuring cups, sports bottles, and baby bottles have marks on the side of the container that allow you to measure the amount of liquid in the bottle. So, if a bottle is labeled at every four ounces or every 100 milliliters, and the contained liquid falls between two labeled points, it becomes important to figure out what amount the unlabeled tick marks represent.  A ruler is another measuring tool that is not always labeled at every increment. In order to get an accurate measurement (for example, to the closest 1/8 of an inch) you must figure out what each mark indicates.

The CyberSquad is faced with a similar challenge when trying to read their thermometer, which is labeled at every ten cyber degrees. The liquid in the thermometer does not reach one of the labeled marks, so they must figure out the incremental increase of each mark in order to determine the temperature. This type of situation may arise in the science lab when measuring liquids. For example, measuring tools such as beakers, flasks, graduated cylinders, and test tubes may be accurate to the nearest milliliter, but perhaps only labeled every fifty milliliters.  Suppose a beaker is marked in this way. To measure approximately two hundred and twenty-five milliliters of water, the water must reach a level halfway between the 200mL and 250mL marks. In this case, there are no other incremental markings, so it is necessary to estimate the measurement halfway between the two points.

Though they may not be precise, these tools are still useful when an approximate measurement is all that is needed. For example, a car speedometer may be marked every five miles per hour. A driver who wishes to remain under a speed limit of 65mph may glance at the speedometer and see that that the needle shows the speed is somewhere between 60 and 65 mph. This estimate is good enough for drivers to know that they are driving at a rate within the speed limit.

To see how meteorologists use weather instruments to forecast the weather, check out Kid Meteorologist QuickTime Video.