diff --git a/README.md b/README.md
index 6e4200b..4c26ba6 100644
--- a/README.md
+++ b/README.md
@@ -23,11 +23,11 @@ go get github.com/kpango/fastime
 
 ## Example
 ```go
-    now := fastime.Now()
+    now := fastime.Now().StartTimerD(context.Background(), time.Millisecond*5)
     defer fastime.Stop()
 
     // Create Instance
-    ft := fastime.New()
+    ft := fastime.New().StartTimerD(context.Background(), time.Millisecond*5)
     defer ft.Stop()
     ft.Now()
 ```
diff --git a/example/result.txt b/example/result.txt
deleted file mode 100644
index 23f028c..0000000
--- a/example/result.txt
+++ /dev/null
@@ -1,16 +0,0 @@
-s1=2022-02-08 22:37:21.754272 +0900 JST
-s2=2022-02-08 22:37:21.754272 +0900 JST
-s3=2022-02-08 22:37:21.754272 +0900 JST
-s4=2022-02-08 22:37:23.755217 +0900 JST
-nanonow 1644327448754453000
-now unixnano 1644327448
-now add unixnano2022-02-08 22:37:29.754453 +0900 JST
-nanonow + dur 1644327449754453000
-string 2022-02-08T22:37:28+09:00
-Address of buf=fuckkkking:	0xc0001c8498
-Address of buf=:	0xc0001c8498
-Address of a1=[102 117 99 107 107 107 107 105 110 103]:	0xc000010350
-Address of b1=fuckkkking:	0xc0001c84c8
-Address of buf=helloooooo:	0xc0001c8498
-Address of a2=[102 117 99 107 107 107 107 105 110 103]:	0xc000010380
-Address of b2=fuckkkking:	0xc0001c84e0
diff --git a/fastime.go b/fastime.go
index 6d4c02a..6479ce4 100644
--- a/fastime.go
+++ b/fastime.go
@@ -22,6 +22,7 @@ type Fastime interface {
 	UnixNanoNow() int64
 	UnixUNanoNow() uint32
 	FormattedNow() []byte
+	Since(t time.Time) time.Duration
 	StartTimerD(ctx context.Context, dur time.Duration) Fastime
 }
 
@@ -167,6 +168,10 @@ func (f *fastime) Stop() {
 	}
 }
 
+func (f *fastime) Since(t time.Time) time.Duration {
+	return f.Now().Sub(t)
+}
+
 // UnixNow returns current unix time
 func (f *fastime) UnixNow() int64 {
 	return atomic.LoadInt64(&f.ut)
diff --git a/fastime_test.go b/fastime_test.go
index 912fdb3..b30cc2c 100644
--- a/fastime_test.go
+++ b/fastime_test.go
@@ -410,16 +410,17 @@ func TestFastime_Since(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			now := Now()
+			f := New().StartTimerD(context.Background(), time.Millisecond*5)
+			now := f.Now()
 			timeNow := time.Now()
-			time.Sleep(100 * time.Millisecond)
-			since1 := Since(now)
+			time.Sleep(time.Second)
+			since1 := f.Since(now)
 			since2 := time.Since(timeNow)
 			if since1 < 50*time.Millisecond {
-				t.Error("since is not correct")
+				t.Errorf("since is not correct.\tfastime.Now: %v,\ttime.Now: %v\tsince1: %d, \tsince2: %d", now.UnixNano(), timeNow.UnixNano(), since1, since2)
 			}
 			if math.Abs(float64(since1-since2)) > float64(50*time.Millisecond) {
-				t.Error("since error is too large")
+				t.Errorf("since error too large.\tfastime.Now: %v,\ttime.Now: %v\tsince1: %d, \tsince2: %d", now.UnixNano(), timeNow.UnixNano(), since1, since2)
 			}
 		})
 	}
diff --git a/global.go b/global.go
index 4f7a4e2..8afa373 100644
--- a/global.go
+++ b/global.go
@@ -47,7 +47,7 @@ func Now() time.Time {
 // Since returns the time elapsed since t.
 // It is shorthand for fastime.Now().Sub(t).
 func Since(t time.Time) time.Duration {
-	return instance.Now().Sub(t)
+	return instance.Since(t)
 }
 
 // Stop stops stopping time refresh daemon
diff --git a/go.mod b/go.mod
index ee70ece..1367cac 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
 module github.com/kpango/fastime
 
-go 1.18
+go 1.20