Calendar Derivation

In order to derive calendars many metrics can be used. Calendars such as Unix time use an epoch and just define a specific point and use a specific unit to calculate time. Many such as the Gregorian calendar use the orbit of the earth around the sun. However, calendars are not always just based on practicality and often are based on cultural and financial policies such as the Igbo which divides the week into different market days. In any calendar however, there will always be some sort of metric and no calendar can be a single solution of all measurements of time.