It is a written code which has seen periodic changes and review, apart from conventions (read customs) of service.

Though it was always subject to considerable seasonal and periodic changes, the current average level is the lowest ever recorded.

The vertical motion forces periodic changes in speed and direction of the air within this air current.

There are also periodic changes in the structure and organization of the church, mainly to accommodate the organization's growth and increasing international presence.

Throughout history, forms of art have gone through periodic abrupt changes called artistic revolutions.

The post was designated as a rotational one to ensure periodic changes in theoretical outlook.

The Sun is not considered a variable star, but it does undergo periodic changes in activity known as the sunspot cycle.

The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth.

It causes a periodic change in the amount of irradiation from the Sun that is experienced on Earth.

However there is no documented evidence that the policy of requiring periodic changes in passwords increases system security.