diff --git a/go/exact/exact.go b/go/exact/exact.go
index f5c3565e..cfc27e09 100644
--- a/go/exact/exact.go
+++ b/go/exact/exact.go
@@ -2,12 +2,14 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package exact implements mathematically exact values
-// and operations for untyped Go constant values.
+// Package exact implements Values representing untyped
+// Go constants and the corresponding operations. Values
+// and operations have unlimited precision.
 //
-// A special Unknown value may be used when a constant
-// value is unknown due to an error; operations on unknown
-// values produce unknown values.
+// A special Unknown value may be used when a value
+// is unknown due to an error. Operations on unknown
+// values produce unknown values unless specified
+// otherwise.
 //
 package exact
 
@@ -38,7 +40,7 @@ const (
 	Complex
 )
 
-// A Value represents a mathematically precise value of a given Kind.
+// A Value represents a mathematically exact value of a given Kind.
 type Value interface {
 	// Kind returns the value kind; it is always the smallest
 	// kind in which the value can be represented exactly.
@@ -379,7 +381,8 @@ func MakeFromBytes(bytes []byte) Value {
 // Support for disassembling fractions
 
 // Num returns the numerator of x; x must be Int, Float, or Unknown.
-// If x is Unknown, the result is Unknown, otherwise it is an Int.
+// If x is Unknown, the result is Unknown, otherwise it is an Int
+// with the same sign as x.
 func Num(x Value) Value {
 	switch x := x.(type) {
 	case unknownVal, int64Val, intVal: