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.