The glasses contain small batteries which must be replaced periodically.

The game also features online leaderboards and challenge levels which are periodically replaced with new ones.

These substances, sold in hardware stores as crystals, need to be replaced periodically.

Some come with filtration cartridges that should be replaced periodically.

On a system with a low number of subscribers, the smartcards can be replaced periodically.

Like all airline parts, the pins are replaced or inspected periodically by the airlines.

Instead, hundreds of rubber balls are attached with reflective tape, which needs to be replaced periodically.

Thus, the acid tanks had to be replaced periodically.

The oil and the oil filter need to be periodically replaced.

In this way almost all the wear of the engaging gears was taken up by the wooden ones and these had to be periodically replaced.