Possible Clues:

• Work on the school map somehow: it’s used to examine pupils
• Work revising the school map: it’s for examining pupils
• Work on the school map, perhaps: it's for examining pupils
• Instrument for inspecting the retina and other eye parts
• See smooth chap lope around -- one to look into your eyes?
• Work on the school map perhaps: it's for examining pupils
• Optical instrument initially marketed in cheap tool shop, perhaps?
• Testing device applied to pupils showing well-focused brightness