Google charts problem

I’m trying to create a line chart using google charts api, but when i use tiny variations as the data it’s not scaling and I am just getting a straight line:

Also, as this is a graph over a 24hr period and when it’s displayed it will be sometime earlier than 24:00, how can i have blank values rather than '0’s…i’d like the graph to just stop at the last data value and be blank for the remaining part of the day?