I just had a wow moment. Last year I stopped using dumb scales which dont save your precious data. I bought a basic Withings wifi scale
Its ok, but fairly basic. Their web page is actually very good (see https://healthmate.withings.com/) and gives good selection of graphs...in fact here is my own weight graph from the last 12 months, totally over 300 measures. Remember with a wifi scale you only need to jump on the scale and it will upload your data automatically to the cloud.
However, I use fitbit a lot, and fitbit has its own wifi scale aria. Its expensive and doesnt have any more features other than body fat : see http://www.livescience.com/49888-best-smart-scale.html. Here is a great comparison of wifi scales from http://www.livescience.com
Anyway it turns out Withings WS30 (and all their wifi scales) connect to fitbit using https://www.fitbit.com/weight/withings#. Just add your Withings account and all your historical data is uploaded to fitbit. Wow so simple. And now you get fitbit weight goals and badges too. Really awesome.