%code 
var
  APos: Integer;
  ANom, ADenom: String;
begin
  result := '%xmp:exif:ExposureBiasValue';
  APos := Pos('/', result); 
  if APos > 0 then
  begin
    ANom := MidStr(result, 1, APos - 1);
    ADeNom := MidStr(result, APos + 1, Length(result));
    if (StrToInt(ADeNom) <> 0)  and
       IsValidNumberString(ANom, '.', False) and
       IsValidNumberString(ADeNom, '.', False)
    then
    begin
      result := 'EV ' + Format('%f', [RoundToPrecision(StrToInt(ANom) / StrToInt(ADeNom), 2)]);
    end;
  end;
end;
%/code