When times prior to the epoch need to be represented, it is common to use the same system, but with negative numbers.
Even systems that allocate more storage to the time representation are not immune from this kind of error.
Other more subtle timekeeping problems exist in computing, such as accounting for leap seconds, which are not observed with any predictability or regularity.
For example, Microsoft Excel observes the fictional date of 29 February 1900 in order to maintain bug compatibility with older versions of Lotus 1-2-3.
Of the only two satellite systems with global coverage, GPS calculates its time signal from an epoch, whereas GLONASS calculates time as an offset from UTC, with the UTC input adjusted for leap seconds.
[6] The following table lists epoch dates used by popular software and other computer-related systems.