Clock/Stop watch implementation to calculate elapsed time between two events.

See more:

C#

ASP.NET

Javascript

SQL-Server

, +

My client had given me a requirement which i want to share with you all and need your suggestion that how i will achieve this.
This is basically a time sheet project where, when ever a user is going for Lunch/Training he will click on a button.My client want that i ll display a big clock or stop watch at that time (The stop watch if implemented not contain start button ,it only have stop button) and all the rest of controls get disabled or the page get gray out and as the user come back he will just stop the Clock/Stop watch and the clock/Stopwatch get disappear/gray out page goes out.
The total time between the two events when the user is on Lunch/Training will be calculated and stored in the database.Please suggest me that how i ll do as i had not implemented this before and this is the first time when i ll work on stopwatch or clock .Please suggest, what i ll implement and how i this requirement get fulfilled.I am using C#,Asp.net and SQl Server.

Awaiting for the response and thanks in advance.