This viewing angle test shows colour bars and grey gradients that make it easy to judge how your screen holds up when viewed off-centre. Look at the patterns straight on, then slowly tilt the screen up, down and to the sides — and watch how much the colours wash out, the brightness drops, or the contrast inverts.
Wide-angle IPS panels stay stable; VA panels shift in contrast and show a gamma change; TN panels shift the most, often inverting from the bottom. It works on any monitor, laptop, phone or TV.