I'm sorry but we can't currently automatically show your previous meter readings when you submit a new one.
However, we've introduced a new online tool, Energy Tracker, to help you record your electricity use over time - just click on the following link www.customerservices.npower.com/app/answers/detail/a_id/285. Please note it's currently for electricity customers with standard meters, but do keep an eye out for gas and Economy 7 electricity versions in the future.