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- When the geopotential height of 700 hPa goes below 2400 m, it is reported 1000 m higher than actual.
When there are significant levels below or equal to 1000 hPa level (i.e. pressure >= 1000), the pressure is reported 1000 hPa less than actual.(this This problem was fixed on effective 2015-08-18T12Z.)When the geopotential height of 1000 hPa goes below MSL, the reported value is same to coded digits in TAC TEMP (512 means-12 m). This problem was fixed effective 2014-02-24T12Z.
The issues are "missing top digit of data", lost in TAC encoding.