Take the cable zero from the shortest delay seen rather than a flag

probe.go

@@ -34,18 +34,20 @@ type cableStats struct {
 	mu      sync.Mutex
 	min     int64
 	samples uint64
+	floor   int64
 
 	txPend map[uint64]int64
 	rxPend map[uint64]int64
 }
 
 type cableView struct {
-	min     int64
-	samples uint64
+	min   int64
+	floor int64
+	ok    bool
 }
 
 func (v cableView) minText() string {
-	if v.samples == 0 {
+	if !v.ok {
 		return "-"
 	}
 	return commasInt(v.min)
@@ -57,15 +59,14 @@ func (c config) cableMetres(views []view) (float64, bool) {
 	if len(views) == 0 {
 		return 0, false
 	}
-	var sum float64
+	var excess float64
 	for _, v := range views {
-		if v.cable.samples == 0 {
+		if !v.cable.ok {
 			return 0, false
 		}
-		sum += float64(v.cable.min)
+		excess += float64(v.cable.min - v.cable.floor)
 	}
-	mean := sum / float64(len(views))
-	return (mean - c.zeroNS) / c.nsPerM, true
+	return excess / float64(len(views)) / c.nsPerM, true
 }
 
 func (c config) cableText(views []view) string {
@@ -114,13 +115,16 @@ func (c *cableStats) put(seq uint64, ts int64, tx bool) {
 	if c.samples == 0 || delta < c.min {
 		c.min = delta
 	}
+	if c.floor == 0 || delta < c.floor {
+		c.floor = delta
+	}
 	c.samples++
 }
 
 func (c *cableStats) view() cableView {
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	return cableView{c.min, c.samples}
+	return cableView{c.min, c.floor, c.samples > 0}
 }
 
 func (c *cableStats) reset() {