This lab explores Weber's law and specifically "Just Noticeable Difference"
Students look at a variety of stimuli and try to notice differences. It is mainly about comparing JND between stimuli.
If you are looking for an activity where your students elucidate Weber's law from their data I do not believe this lab is for you. If you are interested in letting the students experience JND then I think you will be pleased.
It is really just 2 labs and then alternate versions of those labs. I included the versions of labs as I progressed through the directions I wanted to take this lab in case they are at all inspirational.
Try the link before you buy...