This fixes regression bug introduced in
2e20cf9358deb9579ae6a22bc0deb2a772387194

diff --git a/lisp/org-table.el b/lisp/org-table.el
index a7fc863..9724dc2 100644
--- a/lisp/org-table.el
+++ b/lisp/org-table.el
@@ -2513,13 +2513,13 @@ not overwrite the stored one."
                (error "#ERROR"))
           ev (if (numberp ev) (number-to-string ev) ev)
           ev (if duration (org-table-time-seconds-to-string
-                   (string-to-number ev))))
+                   (string-to-number ev)) ev))
       (or (fboundp 'calc-eval)
           (error "Calc does not seem to be installed, and is needed to
evaluate the formula"))
       (setq ev (calc-eval (cons form modes)
                   (if numbers 'num))
         ev (if duration (org-table-time-seconds-to-string
-                 (string-to-number ev)))))
+                 (string-to-number ev)) ev)))

     (when org-table-formula-debug
       (with-output-to-temp-buffer "*Substitution History*"


-- 
Maciek Starzyk