Getting blocks of data from Google Reader API

I have built a basic app using the Reader API but I dont want to retrieve all the items at once to save on bandwidth and processing. I start with the first 50, using

http://www.google.com/reader/atom/user/-/state/com.google/reading开发者_Python百科-list?n=50&xt=user/-/state/com.google/read&r=n

but then I want to get the next 50 once they request it.

I have been playing with tracking the <entry gr:crawl-timestamp-msec=""> but I reckon there's a simpler solution.

How do I do that?

Think I've found the answer myself

use the value <gr:continuation>CArhxxjRmNsC</gr:continuation>

like http://www.google.com/reader/atom/user/-/state/com.google/reading-list?c=CArhxxjRmNsC

for more info read the top answer here How to skip known entries when syncing with Google Reader?