I have a form with a field "quantity" which can have the value "unlimited / infinity":
Quantity: [ ]
What would be a good way to let users enter "infinity"?
1) Tell the user that
-1 means infinity:
Quantity: [ ] (-1 = unlimited)
2) Tell the user that a blank field means infinity:
Quantity: [ ] (blank = unlimited)
3) Radio buttons
() Quantity: [ ] or () unlimited
Any ideas? Or links to related usability studies?