打印机设置SetMapMode(Printer.Canvas.Handle,MM_LOMETRIC); 后字体大小如何控制？(50分)

with Printerdo
begin
begin
Doc;
SetMapMode(Printer.Canvas.Handle,MM_LOMETRIC);

with Canvasdo
begin
//Font.Size:=18;
Font.Height:=68;
end;
.....
对于不同的打印机是否输出结果不一样？怎么能一样呢？