Diagram is missing some features
The diagram tab misses entries on their axes (property and unit) also the numbers on the axes can have up to five digits which can be hard to read if those digits are mostly zeros. Maybe a better representation would help to increase the readability for the diagram.
It seems that an export to the formats like png, jpg or pdf is missing. These exports should be included next to csv and dat.
A nice to have feature would be to change some plot options like marker size, color or type. This is maybe not the most crucial task regarding this software but considering there is so much space below the QComboBoxes for x and y which would host nicely at least some of them seems like a waste