Oh boy that BP is rough, but I suppose that’s what happens sometimes! Ok let’s see.
First, to clean this up you should bring the getter, its connected nodes out through the setter including the clamp and camera boom up over the gate. That way you won’t have crossed wires. Crossed wires make working impossible.
Second, there’s some strangeness around here. I agree that you want to multiply the delta seconds times the “lookuprate” which I guess would be the zoom rate but tying in the section with the camera boom and target arm length I think is where I’m getting confused. You want to set the target arm length to be the lookuprate X deltaseconds X basetargetarm. So if I’m 5000 units away and I zoom at 400 units per second for 2 seconds I’m now only 4200 units away. Then you have to copy and paste that same situation but in the reverse because if I zoom OUT for 2 seconds I should be 5800 units away.
Also, the Gate is not necessary or at least I don’t think it is. I think you may be over-complicating this BP a bit.
However, if you do want to be classy you get set that empty setter you have there to reset your target arm length back to the base value when the joystick is released. That would be neat
Does this help you at all? I think you are getting there, this is definitely the right path.
EDIT: OH dear lord, I just watched that video I linked you. Even Unreal devs suffer in BPs sometimes. Laughing.