Virtualmin Theme version: 7.1
Virtualmin version: 3.69
Operating system: Ubuntu Linux 8.04.2
The timeplot library supports those scales, so it should be fairly easy to have ln(y) based charts. Those are better readable for data with big spikes, like network traffic.
While you're at it: Any chance to have scales on both y axes? It's almost impossible to figure out which value belongs to what data point with more that one set of labels on the left hand axis.