This is a little logic puzzle. There are eight weights, all the same weight except for one which is slightly heavier than the others. The objective is to determine one that is. To help you, you have a balance. Drag weights onto the purple areas on either side of the balance and click "Weigh!" to see which side is heavier, and when you think you've found the heavier weight, click "Guess!" and select the weight you think is the heavier one.
See how few weighings you can use to come up with a strategy that reliably determines the heavier weight. This is based on a job interview question I once came across.