The Technasonic Check Go Pro ball marker is easy enough to use but may take a little practice and time to master.
Here are some trouble shooting tips:
1 - Place it on a table or flat surface
2 - Insert the pen straight into the hole (if the pen is not level, lines may cross)
3 - Do not push the pen too hard, or it will slow down the rotation
4 - For visual aid, rotate the top (where the hole is) 90 degress to the start button and have it level where you can see the position of the pen
5 - Try it with some old balls first to practice
6 - Use new batteries to ensure a fast enough spin rate