| Scale on Cart: Place on the Platform. With Select depressed, you can move the cart along the Platform. You can also move the Platform up and down using click-and-drag motions or the up and down arrow keys. You use the scale on the cart to determine the horizontal force acting on the pendulum ball in the Couomb Lab. For more details, see the Attach & Measure section of the Calibration Lab pendulum & ball help page.