diff --git a/qgate_perf/parallel_probe.py b/qgate_perf/parallel_probe.py
index 919f9bc..d16eedc 100644
--- a/qgate_perf/parallel_probe.py
+++ b/qgate_perf/parallel_probe.py
@@ -2,6 +2,7 @@
 import time
 import os, sys, math
 import json
+
 from qgate_perf.file_format import FileFormat
 from qgate_perf.run_setup import RunSetup
 
@@ -23,10 +24,13 @@ def __init__(self, run_setup: RunSetup, exception=None):
         self.standard_deviation=0
         self.pid = os.getpid()
         self.exception = exception
-
         self.track_time={}
         self.track_time[FileFormat.PRF_DETAIL_TIME_INIT]=datetime.datetime.utcnow()
 
+        # setup default values 1/1/1970 for keys 'TIME_START' and 'TIME_END'
+        self.track_time[FileFormat.PRF_DETAIL_TIME_START]=datetime.datetime(1970,1,1)
+        self.track_time[FileFormat.PRF_DETAIL_TIME_END]=datetime.datetime(1970,1,1)
+
         if run_setup:
             # init incremental calculation of standard deviation
             self.stddev = self.StandardDeviation(ddof=0)
@@ -90,12 +94,13 @@ def _wait_for_others(self, when_start, tollerance=0.1):
 
     def ToString(self):
         """ Provider view to return value """
+
         if self.exception is None:
             out={
                 FileFormat.PRF_TYPE: FileFormat.PRF_DETAIL_TYPE,
                 FileFormat.PRF_DETAIL_PROCESSID: self.pid,
                 FileFormat.PRF_DETAIL_CALLS: self.counter,
-                FileFormat.PRF_DETAIL_AVRG: self.total_duration / self.counter,
+                FileFormat.PRF_DETAIL_AVRG: math.nan if self.counter == 0 else self.total_duration / self.counter,
                 FileFormat.PRF_DETAIL_MIN: self.min_duration,
                 FileFormat.PRF_DETAIL_MAX: self.max_duration,
                 FileFormat.PRF_DETAIL_STDEV: self.standard_deviation,