# External format

External format describes data that has been externally
converted using one of the conversion or processing codes provided
with D3. As a general rule, external format means data is in a human-readable
format.

The main advantage of an internal format is that it takes
much less time to compare two values.

For instance, time values
are converted using the mt input processing code,
which takes a legal external time such as 14:00 (2:00 PM) and calculates
the number of seconds past midnight for this value, resulting in the
internal value. In this case, the internal form would be 50400. The
same mt code used as an output processing code
can be used to convert the internal value to its external form.

Dates are also more easily manipulated if stored in an internal
format. An input processing code of d takes an
external date, use a calculation to determine the number of days that
have elapsed since December 31, 1967 (day 0 on the D3 calendar), and
store an internal julian date. A similar output processing code converts
an internal date to an external form.

In addition, numerical
values are more easily handled by the system if they are all stored
as integer amounts, and the decimal point (if any) is inserted only
upon output. An American dollar amount (for example, $100.00) is converted
upon input to an internal form of 10000 using the mr2 input processing code. A similar output processing code redisplays
the figure as 100.00.

One final reason for using an internal
format is to save storage space (for example, converting the external
form of SMALL, MEDIUM, and LARGE into S, M, and L). The internal values
can then be reconstituted upon output.

## See also

- [d (date) processing code](https://d3codex.com/processingcodes/d-date-processing-code/)
- [Internal format](https://d3codex.com/definitions/internal-format/)
- [mt (mask time) processing code](https://d3codex.com/processingcodes/mt-mask-time-processing-code/)
- [Processing codes](https://d3codex.com/processingcodes/processing-codes/)

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Source: https://d3codex.com/definitions/external-format/ - part of the D3Codex reference.