This example show that, without CAST(),
a SELECT's numeric expression store the result into a NUMERIC field.

It is true ?
If yes, the type double doesn't serve to anything.

Look: strangeNumeric
Another strange thing is that for very great values
(what cannot be represented with a ASCII NNNNNNN.NNNN string)
Does VFP succeed in memorizing in a NUMERIC(20?) the value double.
I have not time to hack the dbf.

CREATE CURSOR tt (ff B)
APPEND BLANK

SELECT ff                      as copyDouble;
       ,1e-19                  as literalDouble ;
       ,CAST(1e-19 as B)       as castLiteralDouble ;
       ,ff+1e-21               as literalexp ;
       ,CAST(ff+1e-19 as B)    AS castExpdouble;
       ,1.2345677888e300       AS strangeNumeric;
        FROM tt INTO CURSOR result

* copyDouble		DOUBLE
* literalDouble 	NUMERIC
* castLiteralDouble     DOUBLE
* literalDouble 	NUMERIC
* castExpdouble		DOUBLE
* strangeNumeric	NUMERIC
CLEAR

LIST STRUCTURE

? TRANSFORM(	copyDouble          ,"@^")
? TRANSFORM(	literalDouble       ,"@^")
? TRANSFORM(	castLiteralDouble   ,"@^")
? TRANSFORM(	literalexp          ,"@^")
? TRANSFORM(	castExpdouble       ,"@^")
? TRANSFORM(	strangeNumeric	    ,"@^")