This paper focuses on the analysis of connection between changes in hard cosmic ray flux (HCRF) and atmospheric pressure. To analyse connection between HCRF and atmospheric pressure change, the data of HCRF were obtained using a gamma spectrometer. The statistical data of measurements have been analysed. Detailed information on atmospheric pressure was presented by the Lithuanian Hydrometeorological Service. Correlation coefficients were calculated by performing a simple linear regression

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... is between HCRF and atmospheric pressure in the same day. A strong inverse correlation during simultaneous measurements was determined. The correlation coefficients were defined for different seasons of the year. An empirical criterion of -20 imp/h was chosen in analysis of HCRF. Connection between HCRF decrease at 1.2-1.6 MeV energy interval and the minimum atmospheric pressure in 3-6 days at individual time intervals is defined in Vilnius. The efficiency of prognosis was 59-73% for the period 2004-2005.