FFP= First Focal Plane = The reticle stays the same subtension no mater what power it is on. In low power the reticle is smaller in high power the reticle is bigger. Takes a little getting used to until you realize you can hold, lead and measure stuff with it.
SFP= Second focal plane = The reticle stays the same size but the picture grows and shrinks around it. Only usefull for holds, leads and measuring on one power. Normally near the the highest power.
Cheers,
Craig6
What did you get?
Cheers,
Craig
I wonāt give back the ACOG until at at least 50 years after the 1911 is trashed, and a decade after Glocks are no more. 
Itās a good sight. Just not as versatile as more modern options.
This is true, the more modern options add weight and complexity (mechanical, and user) and reduce durability, but they do add versatility
I have a question on scope alignment with LPVOs. For my old 30-06 hunting rifle I had the scope professionally mounted/aligned. For a Vortex 1X prism scope that I use on my AR, I secured it where I wanted it, aligned things myself and all is well. I donāt use red dots because of astigmatism. For LPVOs, say out to 3X, how critical is alignment? Is DIY good enough?
What do you mean by alignment? What rifle, mount, and optic? The LPVOās I am familiar with go out to at least 4X and these days most are 6x minimum for the high end, some 8 or even 10.
Do you mean how level the scope is within the mount/rings, relative to the rifle? Alignment is kind of always critical for that so that you can properly adjust windage/elevation cleanly without moving things diagonally, I think itās just a matter of how precise you are trying to be/distance shooting at as to how must it messes you up if itās off.
Iād say the DIY depends on how you did it. The wedges, levels, plumb bob, etc are all viable IME
Yes. That. Maybe shooting out to no more than 200 yards on an AR platform. Maybe a Vortex STRIKE EAGLE 1-6X24. Have not decided on anything for sure.