>I use _screen.properties as public variables, included variables such as totqty, totInv, creditcard, cardnumber, cardholder which go between two forms (invoice, payment).
>
>I got confused when someone told me that in multi-users environment, if two users using the same form in the same time, then one is changing _screen properties for the other, while in my experience, it's not.
>
>I wish I can get more info about it.

_screen is an object scoped to the current VFP (or a VFP executable) session. You can run dozens of these on the same machine at the same time, and each would have its own _screen (and _vfp, for that matter).