With Google’s Science Journal app running in ambient light mode and a bright light overhead, move your finger around the screen of the phone. When you see the reading drop, you have located the light sensor for your phone — we will need to center our later tests over this spot.

Place your phone on a level surface under bright light. If your phone has a case or another accessory on it that won’t let it sit flat, shim it with some cardboard or other easily accessible material.

Measure 1/4 cup of your first liquid and carefully pour it into the clear plastic cup. This is your first sample.

With the sample placed over your light sensor, start recording on your first test. Leave the system to record for a little while to make sure table vibrations or your shadow when turning on the recording isn’t throwing off the reading.

Following the same steps, measure your second sample and compare the two.

Let’s see how incremental changes can affect our readings.

Start by filling your cup with 1/4 cup of water and take a new measurement with the Science Journal app.

Add 1 tsp of salt to your cup and stir until it is fully dissolved. Now take a new measurement.

Continue adding salt, 1 tsp at a time, and take measurements after each until the salt won’t dissolve anymore.