diff --git a/speedtest.go b/speedtest.go
index 43028f9..be82b40 100644
--- a/speedtest.go
+++ b/speedtest.go
@@ -6,6 +6,7 @@ import (
 	"gopkg.in/alecthomas/kingpin.v2"
 	"os"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/showwin/speedtest-go/speedtest"
@@ -151,8 +152,8 @@ func main() {
 				task.CheckError(server.DownloadTest())
 			}
 			ticker.Stop()
-			mean, _, std, min, max := speedtest.StandardDeviation(latencies)
-			task.Printf("Download: %.2fMbps (used: %.2fMB) (latency: %dms jitter: %dms min: %dms max: %dms)", server.DLSpeed, float64(server.Context.Manager.GetTotalDownload())/1024/1024, mean/1000000, std/1000000, min/1000000, max/1000000)
+			mean, _, std, minL, maxL := speedtest.StandardDeviation(latencies)
+			task.Printf("Download: %.2fMbps (used: %.2fMB) (latency: %dms jitter: %dms min: %dms max: %dms)", server.DLSpeed, float64(server.Context.Manager.GetTotalDownload())/1024/1024, mean/1000000, std/1000000, minL/1000000, maxL/1000000)
 			task.Complete()
 		})
 
@@ -187,8 +188,8 @@ func main() {
 			}
 			ticker.Stop()
 			quit = true
-			mean, _, std, min, max := speedtest.StandardDeviation(latencies)
-			task.Printf("Upload: %.2fMbps (used: %.2fMB) (latency: %dms jitter: %dms min: %dms max: %dms)", server.ULSpeed, float64(server.Context.Manager.GetTotalUpload())/1024/1024, mean/1000000, std/1000000, min/1000000, max/1000000)
+			mean, _, std, minL, maxL := speedtest.StandardDeviation(latencies)
+			task.Printf("Upload: %.2fMbps (used: %.2fMB) (latency: %dms jitter: %dms min: %dms max: %dms)", server.ULSpeed, float64(server.Context.Manager.GetTotalUpload())/1024/1024, mean/1000000, std/1000000, minL/1000000, maxL/1000000)
 			task.Complete()
 		})
 		taskManager.Reset()
@@ -200,7 +201,7 @@ func main() {
 	if *jsonOutput {
 		json, errMarshal := speedtestClient.JSON(targets)
 		if errMarshal != nil {
-			return
+			panic(errMarshal)
 		}
 		fmt.Print(string(json))
 	}
@@ -220,6 +221,7 @@ func showServerList(servers speedtest.Servers) {
 }
 
 func parseProto(str string) speedtest.Proto {
+	str = strings.ToLower(str)
 	if str == "icmp" {
 		return speedtest.ICMP
 	} else if str == "tcp" {
diff --git a/speedtest/request.go b/speedtest/request.go
index b9020e3..661514c 100644
--- a/speedtest/request.go
+++ b/speedtest/request.go
@@ -387,6 +387,9 @@ func checkSum(data []byte) uint16 {
 }
 
 func StandardDeviation(vector []int64) (mean, variance, stdDev, min, max int64) {
+	if len(vector) == 0 {
+		return
+	}
 	var sumNum, accumulate int64
 	min = math.MaxInt64
 	max = math.MinInt64
diff --git a/speedtest/server.go b/speedtest/server.go
index 78b3b7f..0a592a4 100644
--- a/speedtest/server.go
+++ b/speedtest/server.go
@@ -42,7 +42,6 @@ type Server struct {
 	Country      string        `xml:"country,attr" json:"country"`
 	Sponsor      string        `xml:"sponsor,attr" json:"sponsor"`
 	ID           string        `xml:"id,attr" json:"id"`
-	URL2         string        `xml:"url2,attr" json:"url_2"`
 	Host         string        `xml:"host,attr" json:"host"`
 	Distance     float64       `json:"distance"`
 	Latency      time.Duration `json:"latency"`
@@ -332,13 +331,14 @@ func FetchServerListContext(ctx context.Context) (Servers, error) {
 func distance(lat1 float64, lon1 float64, lat2 float64, lon2 float64) float64 {
 	radius := 6378.137
 
-	a1 := lat1 * math.Pi / 180.0
-	b1 := lon1 * math.Pi / 180.0
-	a2 := lat2 * math.Pi / 180.0
-	b2 := lon2 * math.Pi / 180.0
+	phi1 := lat1 * math.Pi / 180.0
+	phi2 := lat2 * math.Pi / 180.0
 
-	x := math.Sin(a1)*math.Sin(a2) + math.Cos(a1)*math.Cos(a2)*math.Cos(b2-b1)
-	return radius * math.Acos(x)
+	deltaPhiHalf := (lat1 - lat2) * math.Pi / 360.0
+	deltaLambdaHalf := (lon1 - lon2) * math.Pi / 360.0
+	sinePhiHalf2 := math.Sin(deltaPhiHalf)*math.Sin(deltaPhiHalf) + math.Cos(phi1)*math.Cos(phi2)*math.Sin(deltaLambdaHalf)*math.Sin(deltaLambdaHalf) // phi half-angle sine ^ 2
+	delta := 2 * math.Atan2(math.Sqrt(sinePhiHalf2), math.Sqrt(1-sinePhiHalf2))                                                                       // 2 arc sine
+	return radius * delta                                                                                                                             // r * delta
 }
 
 // FindServer finds server by serverID in given server list.
diff --git a/speedtest/server_test.go b/speedtest/server_test.go
index 9cb4ede..6b48c91 100644
--- a/speedtest/server_test.go
+++ b/speedtest/server_test.go
@@ -1,6 +1,8 @@
 package speedtest
 
 import (
+	"math"
+	"math/rand"
 	"testing"
 	"time"
 )
@@ -26,6 +28,35 @@ func TestFetchServerList(t *testing.T) {
 	}
 }
 
+func TestDistanceSame(t *testing.T) {
+	for i := 0; i < 10000000; i++ {
+		v1 := rand.Float64() * 90
+		v2 := rand.Float64() * 180
+		v3 := rand.Float64() * 90
+		v4 := rand.Float64() * 180
+		k1 := distance(v1, v2, v1, v2)
+		k2 := distance(v1, v2, v3, v4)
+		if math.IsNaN(k1) || math.IsNaN(k2) {
+			t.Fatalf("NaN distance: %f, %f, %f, %f", v1, v2, v3, v4)
+		}
+	}
+
+	testdata := [][]float64{
+		{32.0803, 34.7805, 32.0803, 34.7805},
+		{0, 0, 0, 0},
+		{1, 1, 1, 1},
+		{2, 2, 2, 2},
+		{-123.23, 123.33, -123.23, 123.33},
+		{90, 180, 90, 180},
+	}
+	for i := range testdata {
+		k := distance(testdata[i][0], testdata[i][1], testdata[i][2], testdata[i][3])
+		if math.IsNaN(k) {
+			t.Fatalf("NaN distance: %f, %f, %f, %f", testdata[i][0], testdata[i][1], testdata[i][2], testdata[i][3])
+		}
+	}
+}
+
 func TestDistance(t *testing.T) {
 	d := distance(0.0, 0.0, 1.0, 1.0)
 	if d < 157 || 158 < d {
@@ -33,19 +64,19 @@ func TestDistance(t *testing.T) {
 	}
 
 	d = distance(0.0, 180.0, 0.0, -180.0)
-	if d != 0 {
+	if d < 0 && d > 1 {
 		t.Errorf("got: %v, expected 0", d)
 	}
 
 	d1 := distance(100.0, 100.0, 100.0, 101.0)
 	d2 := distance(100.0, 100.0, 100.0, 99.0)
 	if d1 != d2 {
-		t.Errorf("%v and %v should be save value", d1, d2)
+		t.Errorf("%v and %v should be same value", d1, d2)
 	}
 
 	d = distance(35.0, 140.0, -40.0, -140.0)
 	if d < 11000 || 12000 < d {
-		t.Errorf("got: %v, expected 0", d)
+		t.Errorf("got: %v, expected ~11694.5122", d)
 	}
 }
 
@@ -138,7 +169,7 @@ func TestFetchServerByID(t *testing.T) {
 		if server != nil && (server.ID == id) != b {
 			t.Errorf("id %s == %s is not %v", id, server.ID, b)
 		}
-  }
+	}
 }
 
 func TestTotalDurationCount(t *testing.T) {
diff --git a/speedtest/speedtest.go b/speedtest/speedtest.go
index de00a73..99fde97 100644
--- a/speedtest/speedtest.go
+++ b/speedtest/speedtest.go
@@ -11,16 +11,16 @@ import (
 )
 
 var (
-	version          = "1.6.7"
+	version          = "1.6.8"
 	DefaultUserAgent = fmt.Sprintf("showwin/speedtest-go %s", version)
 )
 
 type Proto int
 
 const (
-	ICMP Proto = iota
+	HTTP Proto = iota
 	TCP
-	HTTP
+	ICMP
 )
 
 // Speedtest is a speedtest client.
@@ -90,6 +90,9 @@ func (s *Speedtest) NewUserConfig(uc *UserConfig) {
 	var icmpSource net.Addr
 	var proxy = http.ProxyFromEnvironment
 	s.config = uc
+	if len(s.config.UserAgent) == 0 {
+		s.config.UserAgent = DefaultUserAgent
+	}
 	if len(uc.Source) > 0 {
 		_, address := parseAddr(uc.Source)
 		addr0, err := net.ResolveTCPAddr("tcp", fmt.Sprintf("[%s]:0", address)) // dynamic tcp port