One or three spectators place them ring on the lock then one of them lock the rings on the padlock.
Then they can form from the 9 cards which are numbered from 1 to 9, 3 three-digit numbers as they want.
The cards are double face cards, on the sides of the cards the value of the numbers and the color of them differ.
Considering both side of the cards there are six different colors and there are from each color 3 numbers.
The spectator can choose the color, the order and the place of the selected numbers. They can vary how they like but if they add with them smart phones the 3 three-digit numbers the total will be the opening combination of the padlock.
