Session Time out on apsx page

Hi all,

I have included this
HttpContext.Current.Response.AppendHeader("Refresh", Convert.ToString(((HttpContext.Current.Session.Timeout * 60) - 10)) & "; Url=Login.aspx?Yoursession=expired")

on all pages, accordingy to one of the post for the redirection
and  this below in web.config file
<sessionState mode="InProc" cookieless="false" timeout="60"/>
Please let me know,
1) What the  http context statement means?(especially this  60) - 10)) )
2) Is it the correct way of including the session timeout and redirection?
3) even if i have given 60 mins and i'm using the page, the session expires.
4) I the above (4) is happening, where else can i look , what could be wrong?
can you please direct me to use the correct way of the page expiration.
Thanks