How do I add values of a field and display rolling total on page?

I have a "Value" field on my site that I can populate when adding an approximate value to the item.  I want to display the total sum of this field in a "Total Value" field at the bottom of every page.  It'll increment automatically every time I add a new item with a specified value.

How do I do this?  What is the formula and where do I put it?

Thanks
Dan
 

hello you mean
1 A text field with a number value that display a number in item view
2 display sum of all value in category view ?

Yes, exactly.  This is driving me nuts.  It should be much simpler to do this than it appears to be!

its not realy simple
need to code it in template
or waiting flexicontent pro plugin to create a field with a little php code for creating a sum