This is Core Activity 6.2 in the HOA curriculum and is titled Estimating Magnitudes Using Interpolation . It is a good introductory activity, teaching students how to estimate just the magnitudes, or apparent brightness, of stars. To estimate magnitudes of variable stars, you will need to interpolate.
Interpolation is the process of estimating a value between two known values.
Near the variable star you will be observing are two or more comparison stars of known magnitude. These stars do not change in brightness and are used to compare the brightness of the variable star. Knowing the values of the magnitudes of the comparison stars and the magnitude range of the variable star itself, you can interpolate or estimate the magnitude of the variable star as it changes over time. Given below are three star fields. The magnitudes of the comparison stars are given.