diff --git a/modules/product/doc/reference.rst b/modules/product/doc/reference.rst
index dfb2d85104..91ee5e8a5c 100644
--- a/modules/product/doc/reference.rst
+++ b/modules/product/doc/reference.rst
@@ -13,6 +13,14 @@ Price
 
    Round the value following ``rounding`` to be stored as unit price.
 
+Units of Measure conversion
+===========================
+
+.. data:: trytond.modules.product.uom_conversion_digits
+
+   A :py:class:`tuple <tuple>` containing the digits to use to store conversion
+   rates or factors.
+
 Product Deactivatable
 =====================