fixed Vis timestamp issue

code/Vis.h

@@ -138,11 +138,17 @@ public:
         }
     }
 
+	uint64_t firstTs = 0;
 	void setTimestamp(uint64_t ts) {
-		static uint64_t firstTs = ts;
+		if (firstTs == 0) {firstTs = ts;}
+		//static uint64_t firstTs = ts;
 		gp << "set label 1 \"" << ((ts-firstTs)/1000.0f) << "\" at screen 0.02,0.98\n";
 	}
 
+	void resetTimestamp() {
+		firstTs = 0;
+	}
+
     void setFilteringMedian(double median){
         gp << "set label 2 \"" << median << "\" at screen 0.02,0.90\n";
     }