Basically, for BT sensor IOs positive values are represented by values from 0x0000 to 0x7FFF (in DEC from 0 to 32767). Negative values are represented by subtracting 65536 from values 0x8000-0xFFFF (32768 to 65535).
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For example the value of the sensor was 64635. In that case, we need to do the following:
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(64635 - 65536) * 0.01 = -9.01 degrees Celsius
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The exact same principle is applied with our 1-wire temperature sensors.

More information: FMIO Parameter List