Changing Bar Graph legend

Hi

Thanks to the flexibility of emoncms I have set up monitoring of rainfall, central heating and solar DC consumption using my own local server.

Apart from tidying and improving my hardware and firmware I would like to be able to change the tool tip legend that comes up when you point to a bar in the graph. At the moment it always shows kWh. 

I realise this must be buried in the code installed on the PI that files would have to be edited. Can anyone tell me where and in which file this is located?

Also as emoncms develops and is used for monitoring many things other than electricity may I request that legends become parameters that can be changed so that  displays can be customized without having to manually edit files when ever there is a software upgrade.

 Regards

Ian