"Constant" property

In v.20 of RSLogix 5000, there is a checkbox to set a tag to be a "constant" in the Tag Properties window. A program I am currently working on is using v.17 and I don't see that checkbox in the Tag Properties. Is that property not available with v.17 or is it selected in a different place?

It probably wasn't available in version 17.

The "constant" property became available in Rev.18 of RSLogix5000, together with the security setting of "External Access" - None, Read Only, or Read/Write.

In Rev.17 the only way to make something as near a constant as you can is to continually (i.e. once per scan) MOV a literal value to it in the code. Doesn't stop it being changed though, just puts it back again if it is changed, but by then the damage could have been done !!