>Position 1 will either be a 4 or a c. 4 indicates a positive number and c indicates a negative.
>
>Position 2 gives the number of decimal points.
>
>The following the following five positions are the actual number.

Given those 7 Ascii characters in cMyStr:
cSign=Upper(Left(cMyStr,1))
nDecimals=Val(Substr(cMyStr,2,1))
cDigits=SubStr(cMyStr,3)
nValue=HexToNumeric(cDigits) / (10 ** nDecimals) * iff(cSign="4",1,-1)

you didnt't say if decimal points is given in hex or not but unless the number has more than 9 decimal places it won't matter. Test:
c200431 would be -10.73