Hi, easy solution could be to do such maths in your custom SQL and alias it as column. Which then can be displayed as grid column. For now i haven't tested such operations on client side.

Is there any way to validate some fields in the edit form, before it is updated on the server side. If there is any solution could me illustrate with an example. Thank you very much.

You can also check http://www.phpgrid.org/docs/ -> Edit Rules for built-in option. If you need custom validation using JS code, It's part of upcoming release of new version. Check your email for example code.