(defun c:midpoint ( / pt1 pt2 pt3 cd os x1 x2 y1 y2 z1 z2)
  (setq CD (getvar "CMDECHO")
        OS (getvar "OSMODE")
  ) ;end setq
  (setvar "CMDECHO" 0)
  (setq PT1 (getpoint "\nFind Midpoint>>  Pick first reference point: ")
        PT2 (getpoint PT1 "\nFind Midpoint>>  Pick second reference point: ")
  ) ;end setq
  (princ "\n ... finding midpoint ...")
  (if (and PT1 PT2)
    (progn
      (if (< (car PT1) (car PT2))
        (setq X1 (car PT1)
              X2 (car PT2)
        ) ;end setq
        (setq X1 (car PT2)
              X2 (car PT1)
        ) ;end setq
      ) ;end if
      (if (< (cadr PT1) (cadr PT2))
        (setq Y1 (cadr PT1)
              Y2 (cadr PT2)
        ) ;end setq
        (setq Y1 (cadr PT2)
              Y2 (cadr PT1)
        ) ;end setq
      ) ;end if
      (if (< (caddr PT1) (caddr PT2))
        (setq Z1 (caddr PT1)
              Z2 (caddr PT2)
        ) ;end setq
        (setq Z1 (caddr PT2)
              Z2 (caddr PT1)
        ) ;end setq
      ) ;end if
      (setvar "OSMODE" 0)
      (setq PT3 (list (+ X1 (/ (- X2 X1) 2)) (+ Y1 (/ (- Y2 Y1) 2)) (+ Z1 (/ (- Z2 Z1) 2))))
      (princ (strcat "\r ... midpoint found at " (rtos (car PT3)) "," (rtos (cadr PT3)) "," (rtos (caddr PT3)) "\n"))
      (command PT3)
    ) ;end progn
    (princ "\r ... function cancelled.  No midpoint found.")
  ) ;end if
  (setvar "CMDECHO" CD)
  (setvar "OSMODE" OS)
  (princ)
) ;end midpoint