Observed signal levels:

 none         DUT3
114.8467    114.8264
114.8445    114.8247
114.8441    114.8261 
114.8457

      averages 
114.8452    114.8257
standard deviations on individual measurements
  0.0012    0.0009
Standard deviations on averages
  0.0006    0.0005
IL = 114.8452 -  114.8257 = 0.0195 dB
Standard deviation 0.0008 dB
Error limits (3 sigma) +/- 0.0024 dB

Errors are estimated from too few data points so
the error estimation for this particular measurement is 
uncertain.
There are many measurements in this series so the statistics
of all the errors estimates will give a good idea about errors.