diff --git a/include/xo/unit/Quantity.hpp b/include/xo/unit/Quantity.hpp
index 2a7f1480..795e2795 100644
--- a/include/xo/unit/Quantity.hpp
+++ b/include/xo/unit/Quantity.hpp
@@ -53,10 +53,14 @@ namespace xo {
             constexpr
             auto rescale(const natural_unit<Int> & unit2) const {
                 /* conversion factor from .unit -> unit2*/
-                auto rr = detail::nu_ratio<ratio_int_type,
+                auto rr = detail::su_ratio<ratio_int_type,
                                            ratio_int2x_type>(this->unit_, unit2);
 
                 if (rr.natural_unit_.is_dimensionless()) {
+                    /* FIXME: rr.outer_scale_exact_ can overflow since fixed precision.
+                     *        accumulate in scale instead
+                     */
+
                     repr_type r_scale = (::sqrt(rr.outer_scale_sq_)
                                          * rr.outer_scale_exact_.template to<repr_type>()
                                          * this->scale_);
@@ -115,9 +119,9 @@ namespace xo {
                 using r_int2x_type = std::common_type_t<typename Quantity::ratio_int2x_type,
                                                         typename Quantity2::ratio_int2x_type>;
 
-                auto rr = detail::nu_ratio<r_int_type, r_int2x_type>(x.unit(), y.unit());
+                auto rr = detail::su_ratio<r_int_type, r_int2x_type>(x.unit(), y.unit());
 
-                /* note: nu_ratio() reports multiplicative outer scaling factors,
+                /* note: su_ratio() reports multiplicative outer scaling factors,
                  *       so multiply is correct here
                  */
                 r_repr_type r_scale = (::sqrt(rr.outer_scale_sq_)
@@ -140,7 +144,7 @@ namespace xo {
                                                         typename Quantity2::ratio_int2x_type>;
 
                 /* conversion to get y in same units as x:  multiply by y/x */
-                auto rr = detail::nu_ratio<r_int_type, r_int2x_type>(y.unit(), x.unit());
+                auto rr = detail::su_ratio<r_int_type, r_int2x_type>(y.unit(), x.unit());
 
                 if (rr.natural_unit_.is_dimensionless()) {
                     r_repr_type r_scale = (static_cast<r_repr_type>(x.scale())
@@ -167,7 +171,7 @@ namespace xo {
                                                         typename Quantity2::ratio_int2x_type>;
 
                 /* conversion to get y in same units as x:  multiply by y/x */
-                auto rr = detail::nu_ratio<r_int_type, r_int2x_type>(y.unit(), x.unit());
+                auto rr = detail::su_ratio<r_int_type, r_int2x_type>(y.unit(), x.unit());
 
                 if (rr.natural_unit_.is_dimensionless()) {
                     r_repr_type r_scale = (static_cast<r_repr_type>(x.scale())
diff --git a/include/xo/unit/scaled_unit.hpp b/include/xo/unit/scaled_unit.hpp
index e529b4ce..41cd4d7e 100644
--- a/include/xo/unit/scaled_unit.hpp
+++ b/include/xo/unit/scaled_unit.hpp
@@ -128,14 +128,11 @@ namespace xo {
             }
 
             /* use Int2x to accumulate scalefactor
-             *
-             * TODO:  rename to su_ratio()
-             *
              */
             template <typename Int, typename Int2x = width2x<Int>>
             constexpr
             scaled_unit<Int>
-            nu_ratio(const natural_unit<Int> & nu_lhs,
+            su_ratio(const natural_unit<Int> & nu_lhs,
                      const natural_unit<Int> & nu_rhs)
             {
                 natural_unit<Int2x> ratio = nu_lhs.template to_repr<Int2x>();
@@ -187,7 +184,7 @@ namespace xo {
         operator/ (const scaled_unit<Int> & x_unit,
                    const scaled_unit<Int> & y_unit)
         {
-            auto rr = detail::nu_ratio<Int, Int2x>(x_unit.natural_unit_,
+            auto rr = detail::su_ratio<Int, Int2x>(x_unit.natural_unit_,
                                                    y_unit.natural_unit_);
 
             return (scaled_unit<Int>
diff --git a/utest/Quantity.test.cpp b/utest/Quantity.test.cpp
index ef9b9694..aaeb6941 100644
--- a/utest/Quantity.test.cpp
+++ b/utest/Quantity.test.cpp
@@ -294,7 +294,7 @@ namespace xo {
                     /* q1/q2, with exact representation (given no fractional dimensions)
                      *
                      */
-                    auto su = xo::qty::detail::nu_ratio<decltype(q1)::ratio_int_type,
+                    auto su = xo::qty::detail::su_ratio<decltype(q1)::ratio_int_type,
                                                         decltype(q1)::ratio_int2x_type>(q1.unit(), q2.unit());
 
                     INFO(xtag("su.natural_unit", su.natural_unit_));
diff --git a/utest/unit.test.cpp b/utest/unit.test.cpp
index 6221b0b5..458a15a2 100644
--- a/utest/unit.test.cpp
+++ b/utest/unit.test.cpp
@@ -44,7 +44,7 @@ namespace xo {
         using xo::qty::detail::nu_product;
         using xo::qty::detail::nu_bpu_product;
         using xo::qty::detail::nu_ratio_inplace;
-        using xo::qty::detail::nu_ratio;
+        using xo::qty::detail::su_ratio;
         using xo::qty::unit_qty;
 
         TEST_CASE("basis_unit", "[basis_unit]") {
@@ -878,7 +878,7 @@ namespace xo {
 
                     log && log(xtag("w.abbrev", w.abbrev()));
 
-                    constexpr auto rr = nu_ratio<int64_t, __int128_t>(v, w);
+                    constexpr auto rr = su_ratio<int64_t, __int128_t>(v, w);
 
                     log && log(xtag("rr", rr));
 
@@ -896,7 +896,7 @@ namespace xo {
 
                     log && log(xtag("w.abbrev", w.abbrev()));
 
-                    constexpr auto rr = nu_ratio<int64_t, __int128_t>(v, w);
+                    constexpr auto rr = su_ratio<int64_t, __int128_t>(v, w);
 
                     log && log(xtag("rr", rr));