--- a/@mp/private/getPrecs.m
+++ b/@mp/private/getPrecs.m
@@ -1,4 +1,10 @@
 function precision =  getPrecs(x, index)
+
+  %# function precision =  getPrecs(x, index)
+  %#   If called with two input values, return the precision of the
+  %#   (one-dimensional) array at given index. If called with only one
+  %#   input value, return an array the same size as x, with the
+  %#   individual precisions.
 
   if (2 == nargin)
     precision = x(index).precision;