why is the angle between the left and right angle reading, double that of the angle of diffraction.
Exact answer not needed but a little help appreciated
many thanks
SG
How does an angle read? Are you sure you chose the right verb?
Angles of diffraction depend upon grating groove spacing. There is no simple "double" rule that I am aware of.
Perhaps if you state the equation that is troubling you, I can help explain.