Let's say that a user has to enter a start date and an end date for some activity, and that activity usually requires a known (default) amount of time (period). To help the user out, let's go ahead and add or subtract the default period when the start date or end date is entered.
Every once in a rare while, the user may want to manually edit both days, not using default period. What kind of control does one use? I've seen (and done) various things in the past but none of them felt really polished and easy. For example, only calculate the value if the field is blank, or detect if the value was manually entered and don't override it. These all required more clicks by the user and wasn't always clear if the default period was used, or if the user manually entered both values.
I'd like to use as little real estate as possible with the least clutter. Here's what I've come up with so far:
The icon indicates the two dates are linked, and the broken link indicates the dates are no longer linked - the default period has been overridden. Is there a more obvious or intuitive way to do this?