for target in MovableMan.Particles(Items) do
　local pardist = SceneMan:ShortestDistance(self.Pos,target.Pos,self.mapwrapx);
　local PX = target.Pos.X - self.Pos.X;
　local PY = target.Pos.Y - self.Pos.Y;
　local VX = target.Vel.X - self.Vel.X;
　local VY = target.Vel.Y - self.Vel.Y;
　local judgeX = PX * VX; --to judge if it's moving toward "self" at X.axis
　local judgeY = PY * VY;
　local UV = -((PX*VX) + (PY*VY))/(PX^2 + PY^2);
　local NX = 2*PX*UV + VX; ---new Vel.X of the target
　local NY = 2*PY*UV + VY; ---new Vel.Y of the target
　local paVel = math.sqrt(VX^2 + VY^2);
------------Another Method
--local angP = math.atan(PY/PX);
--local angV = math.atan(VY/VX);
--local paVel = math.sqrt(VY^2 + VX^2);
--local angCA = angP - (angV - angP);
--local flip = (-1 * spX) / math.abs(spX);
　if target.HitsMOs == true and pardist.Magnitude < (58 + (paVel / 12)) then
　　if judgeX < 0 or judgeY < 0 then ---whether it's moving toward "self"
　　　if target.Vel.Magnitude > 5 then
　　　　if target.ClassName == "MOPixel" then
　　　　　self.counterpar = CreateMOPixel(target.PresetName);
　　　　elseif target.ClassName == "MOSParticle" then
　　　　　self.counterpar = CreateMOSParticle(target.PresetName);
　　　　elseif target.ClassName == "MOSRotating" then
　　　　　self.counterpar = CreateMOSRotating(target.PresetName);
　　　　elseif target.ClassName == "AEmitter" then
　　　　　self.counterpar = CreateAEmitter(target.PresetName);
　　　　end
　　　　self.counterpar.Vel.X = 0.8*NX;
　　　　self.counterpar.Vel.Y = 0.8*NY;
--　　　self.counterpar.Vel.X = ((math.cos(angCA) * paVel) + self.Vel.X) * flip;
--　　　self.counterpar.Vel.Y = ((math.sin(angCA) * paVel) + self.Vel.Y) * flip;
　　　　self.counterpar.Pos = target.Pos;
　　　　self.counterpar:SetWhichMOToNotHit(self,-1);
　　　　MovableMan:AddMO(self.counterpar);
　　　end
　　　self.gloweffect = CreateMOPixel("X-CutTool Shield LittleGlow","X-Region.rte");
　　　self.gloweffect.Pos = target.Pos;
　　　target.ToDelete = true;
　　　MovableMan:AddMO(self.gloweffect);
　　end
　end
end

local UV = -((PX*VX) + (PY*VY))/(PX^2 + PY^2);

If velocity relative to both self and target = 0, then UV = 0
If UV = 0, then new velocity of X and Y are also 0

If position of y and velocity of y are not considered (1-D perspective)

When PX*VX = positive, UV goes into negatives, target traveling away from self,
When PX*VX = negative, UV becomes positive, and target is traveling towards self (ready to be reflected)
As VX increases, UV also increases proportionally and vice versa
Given that VX remains constant (constant X-coordinate movement),
as PX gets closer to 0 (target gets closer to self X-wise), UV decreases.

Purpose of UV for X coordinate appears to be determining velocity X wise