This is for my 10yrs old son. His prescription says he is OS : -5.0(-0.5 cyl) and OD : -0.4( -0.5 cyl). Cm diopter measurements for the printed text 12 pt is OD:40 cm and OS : 43 cm which doesn’t match to prescription. Can some one help where I am going wrong and which one to be considered as a prescription to start for a differential and normalised?
Lighting used for measurements are indoor ambient light.