I am a cancer screening lab tech who uses these pens to mark abnormal cells on
glass microscope slides. My profession has been looking for a white pen that
writes well on glass and fits under the objective lens of the microscope for
thirty years. Finally! A pen that does the job. These are great! They mark
precisely where we want and flow well. The lines show up nicely on the
background of the black microscope stage. Don't ever stop making these or I'll
have to retire...