Are you using Btrieve or ODBC? THe 8 byte FLOAT data type is the Btrieve mapping of the ODBC Double type. Here is the definition from the Pervasive manual:
Caution
Precision beyond that supported by the C-language definitions for the FLOAT (4-byte) or DOUBLE (8-byte) data type will be lost. If you require precision to many decimal points, consider using the DECIMAL type.
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The FLOAT key type is consistent with the IEEE standard for single and double-precision real numbers. The internal format for a 4-byte FLOAT consists of a 23-bit mantissa, an 8-bit exponent biased by 127, and a sign bit, as follows:

A FLOAT key with 8 bytes has a 52-bit mantissa, an 11-bit exponent biased by 1023, and a sign bit. The internal format is as follows: