I posted a project on 28-01-2009 entitled "Charge Meter using a clock". I have now extended its use to measuring electrical energy. Since the mechanical clock integrates increments of watt-hours its principal application is measuring appliances which use current intermittently, such as a refrigerator. For this it does require an external sensor to measure the AC current, and convert to a DC current. I admit these do not grow on trees - I got mine online from a surplus dealer. Sorry I did not include a link to my site in the previous post; here it is:
http://www.worsleyassociates.com/Projects/index.html
http://www.worsleyassociates.com/Projects/index.html