While creating some graphs for my station, I stumbled upon a "cheat" for fixing this graph problem.
For multi-line graphs, imagine that GNUplot draws a series of single-line graphs and then stacks them atop each other to produce the final result. Before the drawing begins, meteohub provides information to the program telling it where to set the minimum and maximum for that axis, and the plotting program uses that information to set the axis for ALL graphs drawn on that side.
Because GNUplot draws lines in sequential order on each graph, this means for certain graph types (bars and impulses), "higher" information often ends up covering up "lower" information. Normally this is a problem, but in this case it provides the solution.
On the left Y-axis, first select th0-max, and give that bar a white color (#ffffff). Then in the second row select the data you are interested in (th0) and give it the red color (see image.)
When you generate the graph, the white data (th0-max) disappears into the background and is unseen, but it provides the needed information to make the values of the left y-axis match the right y-axis and your graph will display correctly!
This trick
should work for most graph types. The important thing to remember is that graph lines are drawn sequentially -- first the left y-axis graphs from top to bottom, and then the right y-axis graphs from top to bottom.
