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Display of fractional numbers is controlled by the `d o`
(`calc-over-notation`

) command. By default, a number like
eight thirds is displayed in the form ‘`8:3`’. The `d o` command
prompts for a one- or two-character format. If you give one character,
that character is used as the fraction separator. Common separators are
‘`:`’ and ‘`/`’. (During input of numbers, the `:` key must be
used regardless of the display format; in particular, the `/` is used
for RPN-style division, *not* for entering fractions.)

If you give two characters, fractions use “integer-plus-fractional-part”
notation. For example, the format ‘`+/`’ would display eight thirds
as ‘`2+2/3`’. If two colons are present in a number being entered,
the number is interpreted in this form (so that the entries `2:2:3`
and `8:3` are equivalent).

It is also possible to follow the one- or two-character format with
a number. For example: ‘`:10`’ or ‘`+/3`’. In this case,
Calc adjusts all fractions that are displayed to have the specified
denominator, if possible. Otherwise it adjusts the denominator to
be a multiple of the specified value. For example, in ‘`:6`’ mode
the fraction ‘`1:6`’ will be unaffected, but ‘`2:3`’ will be
displayed as ‘`4:6`’, ‘`1:2`’ will be displayed as ‘`3:6`’,
and ‘`1:8`’ will be displayed as ‘`3:24`’. Integers are also
affected by this mode: 3 is displayed as ‘`18:6`’. Note that the
format ‘`:1`’ writes fractions the same as ‘`:`’, but it writes
integers as ‘`n:1`’.

The fraction format does not affect the way fractions or integers are stored, only the way they appear on the screen. The fraction format never affects floats.