I have 4 series/variables over time. They are in totally different units (monetary, quantities, elasticities, and percentages). I want to make a line plot for each of them. I know it makes no sense to put in the same graph, not even when using different axes, as they are messy.
What troubles me the most is the selection of the scale of the y-axis (x-axis is time). You can zoom in or out and get visually different degrees of apparent variability of the series (and careless readers might be fooled by this).
Of course, that's why we care about the standard deviation. But still, I want to make a graph of the series alone that are somewhat informative.
My question is: is there some logical scale at which the y-axis is to be presented? For example, do I select the mean and then select the y-axis to cover 2 standard deviations up and down from that mean? Is there some standard here?
PS: I've seen this, this, and this question, but I find no answer to mine there. For instance, the last one, suggested by Nick Cox, has all variables in exactly the same units. In my case, they have for different units. The suggestion of percentage change is not helpful either, because some variables are known to vary much more than others. Ideally, I want to plot the series themselves, and not the changes.