diff --git a/projectnetwork.go b/projectnetwork.go
index 1ae1f1d..e15e58d 100644
--- a/projectnetwork.go
+++ b/projectnetwork.go
@@ -27,18 +27,22 @@ import (
 	"gonum.org/v1/gonum/graph/topo"
 )
 
+// projectNetwork is a directed graph of activity nodes
 type projectNetwork struct {
 	*simple.DirectedGraph
 }
 
+// newProjectNetwork is a constructor for a projectNetwork
 func newProjectNetwork() *projectNetwork {
 	return &projectNetwork{DirectedGraph: simple.NewDirectedGraph()}
 }
 
+// NewNode returns an activity node
 func (g *projectNetwork) NewNode() graph.Node {
 	return &activity{Node: g.DirectedGraph.NewNode()}
 }
 
+// calculateTimes computes the times for each activity in g
 func (g *projectNetwork) calculateTimes() error {
 	sorted, err := topo.Sort(g)
 	if err != nil {
@@ -56,12 +60,15 @@ func (g *projectNetwork) calculateTimes() error {
 	return nil
 }
 
+// forwardPass computes the early times for each activity
 func (g *projectNetwork) forwardPass(toposort []*activity) {
 	for _, a := range toposort {
 		g.setEarlyTimes(a)
 	}
 }
 
+// backwardPass computes the late times and slack for each activity using the
+// early times
 func (g *projectNetwork) backwardPass(toposort []*activity) {
 	n := len(toposort)
 
@@ -75,6 +82,7 @@ func (g *projectNetwork) backwardPass(toposort []*activity) {
 	}
 }
 
+// setEarlyTimes sets the early times for an activity
 func (g *projectNetwork) setEarlyTimes(a *activity) {
 	es := 0.0
 	predecessors := g.To(a.ID())
@@ -86,6 +94,7 @@ func (g *projectNetwork) setEarlyTimes(a *activity) {
 	a.earlyFinish = a.earlyStart + a.duration
 }
 
+// setLateTimes sets the late times for an activity
 func (g *projectNetwork) setLateTimes(a *activity) {
 	lf := math.Inf(1)
 	successors := g.From(a.ID())
@@ -98,6 +107,7 @@ func (g *projectNetwork) setLateTimes(a *activity) {
 	a.slack = a.lateFinish - a.earlyFinish
 }
 
+// an activity represents a task in the project network
 type activity struct {
 	graph.Node
 	dotID       string
@@ -109,6 +119,7 @@ type activity struct {
 	slack       float64
 }
 
+// Attributes returns all the activity attributes to include in the DOT file
 func (a *activity) Attributes() []encoding.Attribute {
 	return []encoding.Attribute{
 		{"DUR", strconv.FormatFloat(a.duration, 'f', 2, 64)},
@@ -120,6 +131,7 @@ func (a *activity) Attributes() []encoding.Attribute {
 	}
 }
 
+// SetAttribute permits reading the duration from the DOT file
 func (a *activity) SetAttribute(attr encoding.Attribute) error {
 	var err error
 	switch attr.Key {
@@ -131,10 +143,12 @@ func (a *activity) SetAttribute(attr encoding.Attribute) error {
 	return err
 }
 
+// DOTID returns the DOTID of the activity
 func (a *activity) DOTID() string {
 	return a.dotID
 }
 
+// SetDOTID sets the DOT ID of the activity
 func (a *activity) SetDOTID(id string) {
 	a.dotID = id
 }