Three measurementsVariable speed belts are sized by top width, side angle and length, and all three must match the drive. The code on the old belt gives these, so use it if you can.
No code?Measure the top width and the thickness, and the length round the outside of the belt. Tell us the make and model of the machine, as variator belts are often specific to it.
Look after the variatorA worn or sticking variator pulley will ruin a new belt quickly. Check the moving flange slides freely and the belt faces are smooth before fitting.