diff --git a/source/Ox/js/Math.js b/source/Ox/js/Math.js
index 8ae31831..9f387665 100644
--- a/source/Ox/js/Math.js
+++ b/source/Ox/js/Math.js
@@ -3,6 +3,8 @@
 /*@
 Ox.acosh <f> Inverse hyperbolic cosine
     Missing from `Math`.
+    > Ox.acosh(1)
+    0
 @*/
 Ox.acosh = function(x) {
     return Math.log(x + Math.sqrt(x * x - 1));
@@ -21,11 +23,23 @@ Ox.asinh = function(x) {
 /*@
 Ox.atanh <f> Inverse hyperbolic tangent
     Missing from `Math`.
+    > Ox.atanh(0)
+    0
 @*/
 Ox.atanh = function(x) {
     return 0.5 * Math.log((1 + x) / (1 - x));
 };
 
+/*@
+Ox.cosh <f> Hyperbolic cosine
+    Missing from `Math`
+    > Ox.cosh(0)
+    1
+@*/
+Ox.cosh = function(x) {
+    return (Math.exp(x) + Math.exp(-x)) / 2;
+};
+
 /*@
 Ox.deg <f> Takes radians, returns degrees
     Missing from `Math`.
@@ -152,14 +166,17 @@ Ox.sign <f> Returns the sign of a number (-1, 0 or 1)
     > Ox.sign(-Infinity)
     -1
     > Ox.sign(-0)
-    0
+    -0
+    > Ox.sign(NaN)
+    NaN
     > Ox.sign(0)
     0
     > Ox.sign(Infinity)
     1
 @*/
 Ox.sign = function(x) {
-    return x !== x || x === 0 ? +x : x < 0 ? -1 : 1;
+    x = +x;
+    return x !== x || x === 0 ? x : x < 0 ? -1 : 1;
 };
 
 /*@
@@ -175,6 +192,8 @@ Ox.sinh = function(x) {
 /*@
 Ox.tanh <f> Hyperbolic tangent
     Missing from `Math`.
+    > Ox.tanh(0)
+    0
 @*/
 Ox.tanh = function(x) {
     return (Math.exp(x) - Math.exp(-x)) / (Math.exp(x) + Math.exp(-x));