Sorry I swore I included the article link?
as far as trifocals, you will still have to raise your chin, and then you begin leaning back and sight acquisition take a lot longer- also the target will be blurred.
When you install the Press On Bifocal on Top of the Dominant eye only, you can walk, work move in complete confidence- I fit a Great deal of Police Officers and Military People with this system and they simply can not afford to take the extra time acquiring sight- they need to have it as instant as possible!
Lets look at an example a customer just got his glasses this last Wednesday afternoon and he thought he would try them out- I told him it could take a bit of time to adjust- a couple times at the range, and he said at 20 yards, he ate the center out of center mass area faster than he has done in years- He asked why I made it sound hard to adjust to, I thought its better I make it sound hard and its easy than if I made it sound easy and it comes up hard!
I have had people try the Trifocals, progressives and Mono Vision - all could and can work for range shooting, however in real time scenes where your have to move and acquire target as quickly as possible, the Trifocals as the Progressive and the Mono Vision ( one eye for distance and one eye for near) makes it hard. A lot of my police officers that have tried the Mono Vision- example had a terrible time trying to read their computers in the cars, It was almost impossible to see on the opposite side of the car, to look down that ally, or the dumpster behind the Drugstore at 2am on a Wednesday night.
There is another advantage of the Press-on style inverted bifocal on top-
I have a customer in St. Louis that will compete in any game he can pull a trigger on- He competes, in IDPA, Ipsc, Three Gun, PPC, Cowboy action, match service rifle and with Black powder- Carl came in one day to get me to adjust his glasses- and I saw 3 sets of marks on the top inside of his frame. I had to ask what made the marks> hevery proudly admitted he did? I had to ask why? he came back with, the 1 set is for most competitions( IDPA< IPSC, Three Gun, Cowboy action, PPC) his eye is centered on the Top bifocal. the next set of markings are moved over about 2-3 milimeters, he uses this group for his match service rifle- the rifle is maybe 1 inch to long for him, and it forces his shoulder back a little and he focusses closer to his nose- His M1 garrand is completely stock and original and he does very well with that setting. the last set is for his Muzzle loader, he competes with an real Antique Muzzleloader, not a kit gun and the stock is too long for him- he has the press on moved as close to his nose as he can get it- the people he shoots with, keep telling him to cut the gun to fit himself and he tells them cut your kit guns all you want, this is a real antique and No body is touching it.
I hope this makes sense- It just help people go back to proper shooting stance and having faster target acquisition! and being safer
If you can see it, you can hit it, If you cant see it, you wont hit it!
Read the article and I hope it helps- maybe I can help you to ask the right questions of your Optician next time your buying something for shooting.