the functions to unpack a +/- b into constituent components.

Jay Bellinger recommended something akin to:

(defun calcFunc-remsdev (a) [remove standard deviation]
 (interactive)
 (cond ((and (consp a)
              (eq (car a) 'sdev))
         (nth 1 a))
        ((and (consp a)
              (eq (car a) 'vec))
         (cons 'vec (mapcar 'calcFunc-remsdev (cdr a))))
        (t
         a)))

(defun calc-remsdev (arg) [get standard deviation]
 (interactive "P") 
 (calc-slow-wrapper
  (calc-unary-op "rsd" 'calcFunc-remsdev arg)))

(defun calcFunc-getsdev (a)
 (interactive)
 (cond ((and (consp a)
              (eq (car a) 'sdev))
         (nth 2 a))
        ((and (consp a)
              (eq (car a) 'vec))
         (cons 'vec (mapcar 'calcFunc-getsdev (cdr a))))
        (t
         a)))

(defun calc-getsdev (arg)
 (interactive "P")
 (calc-slow-wrapper
  (calc-unary-op "gsd" 'calcFunc-getsdev arg)))


But if there is already something else out there, or if you have a better idea, I’d take that instead.

Thanks

Bart