diff --git a/db.go b/db.go
index f2c94c4..f407a39 100644
--- a/db.go
+++ b/db.go
@@ -1,6 +1,10 @@
 package main
 
 import (
+	"errors"
+	"fmt"
+	"log"
+	"strconv"
 	"time"
 
 	"github.com/google/uuid"
@@ -8,17 +12,18 @@ import (
 
 type (
 	db struct {
-		Knowledge Knowledge
-		Users     map[string]User
-		Cadence   []Duration
+		Knowledge knowledge
+		Users     map[string]user
+		Cadence   []duration
 	}
-	Knowledge struct {
+	knowledge struct {
 		Questions map[string]Question
 		Answers   map[string]Answer
 	}
-	User struct {
+	user struct {
 		History map[string][]History
 	}
+	duration time.Duration
 )
 
 func (db db) HistoryOf(user string) map[string][]History {
@@ -84,3 +89,45 @@ func (db db) lastTS(user, q string) time.Time {
 	}
 	return time.Unix(0, max)
 }
+
+func (d duration) MarshalYAML() (interface{}, error) {
+	log.Println("marshalling duration", time.Duration(d))
+	return time.Duration(d).String(), nil
+}
+
+func (d *duration) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var s string
+	if err := unmarshal(&s); err != nil {
+		return err
+	}
+	count := ""
+	var ttl time.Duration
+	for i := range s {
+		if s[i] < '0' || s[i] > '9' {
+			n, err := strconv.Atoi(count)
+			if err != nil {
+				return err
+			}
+			count += s[i : i+1]
+			switch s[i] {
+			case 'w':
+				count = fmt.Sprintf("%dh", n*24*7)
+			case 'd':
+				count = fmt.Sprintf("%dh", n*24)
+			}
+			d, err := time.ParseDuration(count)
+			if err != nil {
+				return err
+			}
+			ttl += d
+			count = ""
+		} else {
+			count += s[i : i+1]
+		}
+	}
+	if count != "" {
+		return errors.New(count)
+	}
+	*d = duration(ttl)
+	return nil
+}
diff --git a/main.go b/main.go
index cbb5ca2..33633fb 100644
--- a/main.go
+++ b/main.go
@@ -2,11 +2,9 @@ package main
 
 import (
 	"bufio"
-	"errors"
 	"fmt"
 	"log"
 	"os"
-	"strconv"
 	"time"
 
 	"gopkg.in/yaml.v2"
@@ -36,7 +34,6 @@ type (
 		TS   int64
 		Pass bool
 	}
-	Duration time.Duration
 )
 
 func main() {
@@ -91,43 +88,3 @@ func NewDB() (DB, error) {
 	}
 	return db, nil
 }
-
-func (d Duration) MarshalYAML() (interface{}, error) {
-	return time.Duration(d).String(), nil
-}
-
-func (d *Duration) UnmarshalYAML(unmarshal func(interface{}) error) error {
-	var s string
-	if err := unmarshal(&s); err != nil {
-		return err
-	}
-	count := ""
-	var ttl time.Duration
-	for i := range s {
-		if s[i] < '0' || s[i] > '9' {
-			n, err := strconv.Atoi(count)
-			if err != nil {
-				return err
-			}
-			count += s[i : i+1]
-			switch s[i] {
-			case 'w':
-				count = fmt.Sprintf("%dh", n*24*7)
-			case 'd':
-				count = fmt.Sprintf("%dh", n*24)
-			}
-			d, err := time.ParseDuration(count)
-			if err != nil {
-				return err
-			}
-			ttl += d
-			count = ""
-		} else {
-			count += s[i : i+1]
-		}
-	}
-	if count != "" {
-		return errors.New(count)
-	}
-	return nil
-}