If you have multiple bikes you’re trying to setup the fit identically on do the following.
For the second bike you’re trying to dial in use your “good bike” to get the following measurements and then apply them to the second bike: (Make sure you buy the same model saddle for the second bike. This assumes your crank length is also identical, otherwise you’ll need to account for the shorter/longer crank length in your measurements. Easy to do but just be aware)
Make sure to adjust your aerobar pad angle, extension angle and length on your second bike before you start.
Stand the bike up vertically on a level floor, put the back tire against the wall, and take the following measurements:
Saddle setback:
- Measure from the wall to the center of the BB
- Measure from the wall to the tip of the saddle
Subtract those to get your setback
Saddle height:
- Measure from center of BB to the identical place on both saddles.
***Note if your seat tube is not vertical you may have to iterate on this a couple of times on the second bike to get it exactly the same. It doesn’t take long though.
Stack:
- Measure from floor to center of BB vertically
- Measure from floor to aerobar pad. Subtract and that will give you stack
Reach:
- Measure from wall to center of aerobar pad
- Subtract that from your wall to center of BB measurement and you’ll get your reach
Those are your key measurements.
You can also apply this to road bikes, just replace aerobar pad to where you grip on the hoods and measure from there. 
Hope this helps!
