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When generating rotation by a simple multiplication, say frames A and a multiplication factor of B (for degrees), the total rotation at any frame is rotation angle = A * B degrees (could be using time secs, but it's the same math) If B is constant, the total rotation increases linear with time (frames) ie at a constant speed. Say you were at 50 frames (A) with multiplication factor (B) of 10 degrees, the total rotation is A * B = 50 * 10 = 500 degrees at F51 A * B = 51 * 10 = 510 deg etc But if at F50, you try to slow down the rotation speed by dropping B to 9 degrees (B keyframed 10 at F50 and 9 at F51), the total rotation at F51 is A * B = 51 * 9 = 459 degrees so the object has gone backwards ! (this is your glitch) whereas my method of adding a smaller value in that frame, still goes forward. If I was generating rotation by adding 10 degrees per frame, the rotation is angle at F50 = 500 degrees then I lower the speed to 9 angle at F51 = 509 degrees angle at F52 = 518 degrees > still going forward, but slower Simplifying this using linear speed - if an object is at 100m and after 1 sec it is at 105m, its speed is 5 m/s ie 5 is the change in the existing value in one second. When the object is at 200m, 1 sec later (if still going at the same speed) it will be at 205m. The speed is the change per unit of time - the distance increases by the same amount ie 5m in 1s. With my 'addition method' of generating rotation speed, the time unit is 1F and I'm adding a set value every time unit - 1F or 1/30 sec. If I want to vary the speed by changing the amount added per frame, I'm adding to the existing rotation. If I add a smaller amount, the object goes a bit slower - not backwards. If I add the same amount every frame, it has constant speed, if I add a larger value every frame it goes faster. If I add zero - it stops. TLDR version > speed is the rate of change per unit of time. edit : see demo of linear speed by addition https://www.dropbox.com/s/7znmbmo7c0zu0y7/demospeed.c4d?dl=1

Maybe not relevant to the flip display issue, but here's a little trick of mine to get varying rotation speed without glitches. Using time + multiply is fine for constant speed, but if you generate rotation by adding a small amount every frame, you can change the amount added and get smooth speed changes. There's a rotation reset @ F0, otherwise the rotation value persists. Also, since this is an addition, any viewport activity (moving stuff or just clicking) when F > 0 will cause the XP to recalculate and rotate the object 1 step - but realigns when timeline is rewound to F0. I used radians in the XPresso to save unnecessary degree conversion. https://www.dropbox.com/s/bx6ibid34colx2x/addrotate.c4d?dl=1 method works well with helicopter rotors if amount added keyframed https://www.dropbox.com/s/azjzi3lnr7f794q/chopper.c4d?dl=1

@Gregor check this :

this is what I get so far . the problem is when the speed values is different it will have some glitch animation . I will try to find a solution for this , it would be helpful if other members can share there opinion on how to fix this rotation.c4d.zip