How do I get the distance between 2 3d points?

Okay... I got it to work... but now I have a new problem...

If rise = 1 Or low = 1
	'DebugStop
	Local pick:Tentity = CameraPick(cam.cam,EventX(),EventY())
	If Not pick = 0
	Local px:Float = PickedX()
	Local py:Float = PickedY()
	Local pz:Float = PickedZ()
	Local pnx:Float = PickedNX()
	Local pny:Float = PickedNY()
	Local pnz:Float = PickedNZ()
	Local ptriangle:Int = PickedTriangle()
	Local psurface:Tsurface = PickedSurface()
	Local pentity:tentity = PickedEntity()
	Local p1:Tpivot = CreatePivot()
	PositionEntity(p1,px,py,pz)
	Local p2:Tpivot = CreatePivot()
	For Local i:Int = 1 To psurface.no_verts
		Local vx:Float = VertexX(psurface,i)
		Local vy:Float = VertexY(psurface,i)
		Local vz:Float = VertexZ(psurface,i)
		PositionEntity(p2,vx,vy,vz)
		Local dist:Float = EntityDistance(p1,p2)
		If dist <= Float(GadgetText(ModifyTerrainWnd_TextField_Amount))
			If low = 1
				MoveVertex(psurface,i,0,-0.1,0)
			ElseIf rise = 1
				MoveVertex(psurface,i,0,0.1,0)
			EndIf
		EndIf
		Next
	EndIf
EndIf

This inside of a EVEN_MOUSEDOWN
th ideea is that when I click on a plane the vertices that are in a set amount of distance move down or up... I ckeck for every vertice the distance between it and the pickedx,y,z... the vertices do move up or down... but in some cases some vertices that are at a bigger distance and at the margin of the plane(important) also move up or down