it’s not 8 tweened frames, in the “Animation Tools” if you scroll down to the bottom you’ll see some text, read it

it limits the tweened frames to keep the fps at 60

10fps @ 8 tweened frames is impossible, so it lowers it to 5 (and the math makes it 60fps)

16fps @ 8 tweened frames is impossible too, the max tweened frames for 16fps = 2 (and the math makes it 48fps)

anything above 20fps has a max tweened frames of 1

anything above 30fps can’t be tweened

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basically read the text under all the stuff in “Animation Tools”