+(defun org-estimate-mean-and-var (v)
+ "Return the mean and variance of an estimate."
+ (let* ((low (float (car v)))
+ (high (float (cadr v)))
+ (mean (/ (+ low high) 2.0))
+ (var (/ (+ (expt (- mean low) 2.0) (expt (- high mean) 2.0)) 2.0)))
+ (list mean var)))
+
+(defun org-estimate-combine (&rest el)
+ "Combine a list of estimates, using mean and variance.
+The mean and variance of the result will be the sum of the means
+and variances (respectively) of the individual estimates."
+ (let ((mean 0)
+ (var 0))
+ (mapc (lambda (e)
+ (let ((stats (org-estimate-mean-and-var e)))
+ (setq mean (+ mean (car stats)))
+ (setq var (+ var (cadr stats)))))
+ el)
+ (let ((stdev (sqrt var)))
+ (list (- mean stdev) (+ mean stdev)))))
+
+(defun org-estimate-print (e &optional fmt)
+ "Prepare a string representation of an estimate.
+This formats these numbers as two numbers with a \"-\" between them."
+ (if (null fmt) (set 'fmt "%.0f"))
+ (format "%s" (mapconcat (lambda (n) (format fmt n)) e "-")))
+
+(defun org-string-to-estimate (s)
+ "Convert a string to an estimate.
+The string should be two numbers joined with a \"-\"."
+ (if (string-match "\\(.*\\)-\\(.*\\)" s)
+ (list (string-to-number (match-string 1 s))
+ (string-to-number(match-string 2 s)))
+ (list (string-to-number s) (string-to-number s))))