On the 5m, 30m and 1h views the graph plots one point per second, so the shape of the graph line already shows the jitter. A flat line means there's none, even if the latency is high. A sawtooth line means there's plenty, and the jitter is roughly the height of the teeth, top to bottom.
On the 24h and 7d views each point is an average of a whole minute or hour, so the jitter info gets smoothed away. To display it, we've added a popup in the
latest build: hover the mouse over the graph and a crosshair follows the cursor, showing the range for the period under it, with the fastest and slowest reply in that period. For example, "17 ms (12-53)" means the period averaged 17 ms, the fastest reply was 12 ms, the slowest 53 ms, and the gap between the two is your jitter.
The table above the graph has a Jitter column as well. That's the live figure, the average change from one ping to the next.