Like others, thanks very much for posting this, it’s been really, really useful.
I had a bell transformer with 4/8/12v terminal options, so replaced it with the CUB1 and wired into the 24v terminal. With non-touching bare wires at the switch end of the circuit and the old switch removed, I measure 25v on the output of the transformer, 22v on the existing (very old) mechanical chime, and still 8–10v (it varies, which worries me) at the bear wires where I’ve disconnected the old simple doorbell switch. I’m concerned the transformer replacement hasn’t upped the voltage before I even open the Nest Hello cellophane! Is the chime “holding it back” if a chime has a certain voltage rating? Is the wiring from chime to the switch bad (if so I’m screwed because it’s all been built around during a porch extension so its not serviceable). Or do I need to start installing the Nest chime connector before I can take a proper voltage reading at the switch wires? Any ideas greatly received!
UPDATE: I went “yolo” on it, this update could be useful for anyone in the situation I faced. Initially I installed just the Hello itself to see if the multimeter was correct, and it came up yellow light, no surprise with the reported 8–10v. I removed the Hello, then I followed the instructions and installed the chime connector first, then re-installed the Hello. Blue light! Voltage across the wires into Hello measures 22v, it all works fine. Happy days!