Setting the attribute value for a usercontrol

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Silverlight4

I am using this sample provided in this website from scottlogic.
http://www.scottlogic.co.uk/blog/colin/2010/10/developing-a-lookless-silverlight-gauge-control-part-2/

Thanks for a really great sample. I am new to silverlight, I have another usercontrol where I am placing these guage and bullet usercontrols and I also have a textbox and button. When I click the button I would like to set the needle based on the textbox value for the radial guage and bullet graph. How do I do that?

Please give me some advice!

Thank you.