diff --git a/decor/speed.go b/decor/speed.go
index 9516fdf..9db4ea8 100644
--- a/decor/speed.go
+++ b/decor/speed.go
@@ -84,6 +84,7 @@
 
 func (d *movingAverageSpeed) Decor(s Statistics) (string, int) {
 	var str string
+	// ewma implementation may return 0 before accumulating certain number of samples
 	if v := d.average.Value(); v != 0 {
 		str = d.producer(float64(1e9) / v)
 	} else {