p n is the polarization with no bottle present with the current system changes in polarization can be measured to better than one part in 10 000 or better than 0 01 this data is saved in a data file along with other information such as time data comments background level average level etc l the slope of the relation rp i as a function of angle is examined and areas of relatively large changes of slope are categorized as point defects these regions are eliminated from the data by replacing them with a straight line going from the point proceeding the region in question to the first point after that region to give rpm i m the low frequency portion of the relation rp i is calculated be applying a digital lowpass filter to the data with the point defects removed rrm i the cutoff of this filter is currently 200 points this is equivalent to a spatial wave length of 40 u00b0 rlf i will be used to reference this low frequency portion of the relation n the spatial spectral energy of rrm i around the bottle is calculated by determining the root mean square of the data with the point defects removed the high frequency portion of the relation is found by subtraction the low frequency portion rlf i from the whole rrm i the energy for this relation rhf i containing spatial frequencies less than 40 u00b0 in extent high frequency stress is determined by using root mean square relation m the various forms of rp i are plotted on the computer monitor for realtime examination by an operator these include the.