A Vision Aid from Phone-Grade Parts: What Magnification and Contrast Actually Buy

SIMULATED, NOT MEASURED. A performance budget for a phone-grade vision aid used as a reading and label-checking instrument, modelled from stated assumptions (phone-class camera and screen; medicine-label, newsprint, bill, and dial tasks; acuity 20/70 to 20/400). Field of view, not pixelation, is the binding limit: the phone with a fixed stand and 500 lux lamp (GBP 35 / USD 40) serves 20/70 and 20/100 on all tasks, serves 20/200 marginally for short checks, reads dials at every level, and cannot serve sustained reading at 20/400. Hand-held tremor, non-uniform glare, and curved bottles are quantified as failure cases. All numbers are produced by the deposited compute.py.