When you say "more (older) data" I assume you want to read from the history of the
cpu dataport, not other dataports, right?
If you need to use the device HTTP data API, you can use the features from the long-polling features to read data from the past: http://docs.exosite.com/http/#long-polling Specifically look at the
If-Modified-Since header, you can set this to how ever far back you want to read then progressively move it forward, reading one point at a time.
That method will be rather slow to read large amounts of data, I'd suggest instead to the the RPC API's
read procedure. With that you can read large amounts of the history at a time. See the docs for that here: http://docs.exosite.com/rpc/#read