Each round works like this:

• First you see the original video alone. Watch it play through once.
• Press Show A and B — two altered versions appear; the original is not shown with them.
• Once A and B have played through once, pick the version that is truer to the original — the one you would accept as a faithful copy. Click it, or use the ← and → keys.
• Press ↑ any time to see the original again, and ↑ to come back.
• Anything counts: missing or changed things, blur, blockiness, timing.
• There is no "equal" answer: if they look alike, choose the one you think is truer.
• Changed your mind? Click an earlier square in the top strip to go back and revise that answer.

One round is 40 choices and takes about 25 minutes, because every video plays through once before you go on. There are no right or wrong answers except a few obvious check questions.

Participation is anonymous and voluntary. We store only your choices, response times, and browser type. By starting you agree to this use.

Name or nickname (required) Use the same name each time and you carry on where you left off — you will never be shown a comparison you already answered. A different name counts as a different person, so two people can share one computer. A name already used on another browser or device cannot be used again — pick one that is yours. Start