My piano teacher always talked about tempo with an old style metronome.   

3:1 on full shots, lest anyone try to hit a driver at a 2:1 ratio.

I have been thinking a bit about this post since I’m really focusing on improving my putting until the season really starts over here. 
 

I have now added a metronome to my practice. 
 

Now on to my question - I have read multiple places that a number to aim for (although not absolute but it’s something I can quantify) is 600ms on the backswing and 300 on the downswing. 
 

Now reading this post and adding the 78BPM to the equation a beat with 78BPM is roughly 770ms so that doesn’t help me at all. If you wanted a 600ms beat that would be 100BPM exactly. But since it’s easier for me to count 1 - 2 on the back and then 3 on the downswing, to get that beat you’d need to set the metronome to 200BPM so one beat is 300ms. So you go 1-2 end of backswing and 3 on impact. But that 200BPM beat is just so fast that it makes me nervous. 
 

So right now I’m practicing with 100BPM and I go full backswing with one and the full downswing (till it stops on the follow through) on two. What are your thoughts on the way I approached it?

But isn’t the downswing measured right until impact?

Hmmm... I've never actually thought of my putting stroke in that way, but... it makes sense.  

I have equated my putting stroke to a video game meter.  I know how far back I need to bring the putter head for a 10 foot putt, 20 foot putt, etc.  The problem is, I seem to pull a lot of my putts.  Perhaps I've been too focused on the 'where' of my putter head instead of the 'when' aspect.  

CY

What about loading the driver?  3:1 sounds about right.