How can I use a single check box to identify if an particular scenario exists or not? Think of it as ON or OFF.

For example -
The form has the following Question:
Is this a Duplicate Item? ( )

If there is no duplicate, there'd be no check in the checkbox. In this case, I'd want to write a 0 to the database upon Form Save.
If there is a duplicate, there would be a check in the checkbox. In this case, I'd want to write a 1 to the database upon Form Save.

Any thoughts?

Please note that you can use custom coding in the "Items" section of the checkbox group. More details are available here:

http://www.rsjoomla.com/support/documentation/view-article/57-components.html

How do I default a single checkbox to "checked"?

You can use the following command [c] on the line you want to be the default.
For example, in a radio group enter your list
-10
-5
0 [c]
5
10
When the form displays the "0" button will be selected. The user could then click on any other button and change the selection. The command also works with other components.
Hope this helps.

... Radiogroup radio checked selected syntax ...

There seem to be a lot of answers to the question of "how to I set a radio button to be initially enabled" - up to using onFocus scripts which detect if it's an intial doc load ...

1. This FAQ solution may apply okay for checkboxes and dropdowns. But, it fails to work for radio groups (www.rsjoomla.com/support/view-article/12...s-and-dropdowns.html)

Namely, Paris{checked}|Paris ... does not appear to work in my version of RSForm Pro (v1.3.0R36 in J1.7.3)
... but it's partly useful/correct in setting different values for the field Name and Label

2. The javascripting solutions mentioned elsewhere in the forums just to set the initial state to checked are a) unnecessary and b) overkill to set the initial check state of a radio button

Anyway ...

I have a form which gathers contact info: Phone, Email ... and then a radio group which indicates visitor's preference for being contacted (ie, Phone or Email)

For various reasons, we want the field names to be unique - ie, the name of the Phone textbox control shouldn't conflict with the Phone radio control's name.

Sooo ...
1. I use part of the info from the FAQ above - namely the "|" syntax
2. I use the "[c]" command notation mentioned in the previous post to set the initial checked state

In the items section, I have:
PrefPhone|Phone [c]
PrefEmail|Email

The radio control is named "PrefPhone" but the label displayed to the visitor is "Phone" ... and Phone is initially checked enabled.

If it works correctly, the radio control should appear checked in the RSForm manager (admin) ... as well as when you load your form on your web page.

Hope that helps.