How to control type of history graph?

Hi, I have two values I want to show in a graph. One is a sensor value (temperature) and one is a calculated value, stored as variable (with the variable custom_component).

The problem is that the value from variable is shown as kind of interpolated graph (angular lines), whereas the temperature from sensor is shown as step graph (rectangular lines). You can see it in the screenshot below:

As you can see, both have a unit of measurement and are shown as graph. But I would like to show the below one also as step graph.

Is there a setting or based on which attributes does the history-graph card decide how to draw the graph?

Something I would like to know as well.
I have a fan which sends an update on a speed change, therefore the graph looks horizontal until the speed change when it changes from the previous point ot a slope as if the change took place gradually.

oops, did miss the 2020 part…