HP 39g+ - Manual (Page 35)

Getting started 1-25
Setting
fraction
precision
The fraction precision setting determines the precision in
which the HP 39G/40G converts a decimal value to a fraction.
The greater the precision value that is set, the closer the
fraction is to the decimal value.
By choosing a precision of 1 you are saying that the fraction
only has to match 0.234 to at least 1 decimal place (3/13 is
0.23076...).
The fractions used are found using the technique of continued
fractions.
When converting recurring decimals this can be important.
For example, at precision 6 the decimal 0.6666 becomes
3333/5000 (6666/10000) whereas at precision 3, 0.6666
becomes 2/3, which is probably what you would want.
For example, when converting .234 to a fraction, the precision
value has the following effect:
• Precision set to 1:
• Precision set to 2:
• Precision set to 3:
• Precision set to 4