Input Fractions of an Inch

A form control should allow users to input a length accurate to 1/32 of an inch.

The users are used to working with fractions of an inch (rather than decimal places). However, I plan to store the data with decimal places for calculations, sorting, etc.

Plan:

• Provide a text box for input.
• The user can enter the number in either format (fractional or decimal).
• The control would flag an invalid input: invalid format, a number not a multiple of 1/32 of an inch
• A valid number would then be displayed in both formats (simplified fractional and decimal)

Does my plan have any obvious caveats?

Should I consider an alternate control: require decimal entry, 32-tick slider for the fractional part, three textboxes (integer, numerator, denominator), etc?