Improve documentation.

main.go

@@ -40,8 +40,11 @@ import (
 //   An average month has 2 629 743.83 seconds.
 //   This saves at least:
 //     2,629,743.83 seconds * 4 bytes = 10,518,975.32 bytes = 10,518.98 kB = 10.52 MB
-//   This applies both to Dt1 and Dt2 as well as Rt1 and Rt2, so should be quadrupled.
-//     10.52 * 4 = 42.08 MB.
+//   This applies both to Dt1 and Dt2 as well as Rt1 and Rt2, only one is recorded at a time.
+//     10.52 * 3 = 31.56 MB.
+// In addition, many meters only update these metrics once every 10 seconds,
+// meaning even more storage capacity is saved:
+// 10.52 / 10 * 9 = 9,468 MB.
 
 type Payload struct {
 	T   string `json:"t"`   // Timestamp