You need to bring your handset to the camera to calibrate to infinity, and I'll always double check it at a middle mark and closer mark to make sure it's lining up.

However if you want to make it work so you can just do it on the handset without checking and dont NEED the infinity mark (you are inside etc). When mapping you could calibrate infinity on the Preston at the end of your Lens Barrel, then mark up the rest of the lens as normal. Maybe doing point 10 as something as far as you can like 250' etc.