The balls undergo a variety of tests to determine that they have similar physical characteristics. The goal, say lottery officials, is to ensure that every jackpot number is a truly random occurrence.

The balls are first checked with a micrometer to determine that they are in fact 50 mm in diameter, as they should be. Next they are measured for resiliency (how well they bounce). This can be done using a measuring device known as a resiliometer, which drops a weight on the ball and measures how far away it is propelled, or by videotaping the balls as they are dropped and measuring the height of their bounce.

The balls are then submerged in water, and their volume determined by how much liquid is displaced. The test subjects are even exposed to an x-ray examination to ensure that there are no impurities or cavities within their solid rubber spheres.

Then once the mass of the balls is measured, they are ready for the machine. The balls are allowed to be within five per cent of variation for each test.