I develop a monitoring tool for applications, and one of the upcoming feature is a new "Latency Chart". This chart is made automatically as a jpg file, and it represents the latency of a given host for the last 24 hours (i.e. how many mili-seconds it takes to communicate from my host to the given host). It polls and collects data every minute.
Right now it looks like this one:
Well I have the following doubts and I'd like to ask what you think about:
a. It currently represents 3 modes: Up (then we show the latency metrics); Down (the given host in unreachable) and Unknown (times where the application is not polling and measure latency). Since both "Down" and "Unknown" states means 0 in latency, we can't distinguish them if the Y pivot starts at 0, so we put negative values of the Y pivot, so we can color red for "Down" and White\gray for "Unknown". It helps distinguish them, however I'm not sure if providing negative values in such graph is clear enough. I consider to unite them both to one state, named "Down or Unknown" so the Y pivot contains positive values only (starting from 0) and it probably helps the chart to be more clear. What do you think about?
b. Do you think that a line chart might be better than this bar chart (for that latency purpose)? Actually there's no need to color the area below latency values, so I'm wondering if it makes this chart more readable and clearer.