Steven,

set soapbox on

In general it's bad OOP to me mucking around with the internals of another object, you are breaking the encapsulation part of OO.

The outside world should talk to the form and the form should then do the talking to its objects. You can expose a nTimerInterval property of the form that can be set from the outside and use an assign method on the property to have it update the timer's interval. You could also use a form method that can be called. Personally I like the ease of working with property based interfaces where I can.

>If I create a timer class in my project. Then I use this class on a form. How can I programatically control the interval property outside of this form?