Simply enter the maximum weight you have lifted in an exercise, the reps you have done in the exercise and press the "calculate" button.
In addition, having a registered account allows you to log in to another device and still view and update your maximum weights.
With Max Weights you can keep track of your strength development in weightlifting, weightlifting or crossfit exercises, with bars or dumbbells.
Choose an exercise, add the maximum weight used and the repetitions you have done.
Another option is to continue without registering, but if you sign out, all the weights you've added will be lost since you're logging in anonymously and couldn't retrieve that data.