What's a "flight computer?" Does that make the aircraft fly and stuff?
Usually I use the look and swag method. In flight school, after API and RI ground school, I just used a plotter, and calculator when I needed a conversion. It's so much faster and much more accurate. When flying now, I just put a "Fly-To" on where I want, and it tells me how long. Someone whipped out a CR=2 the other day. It was like a lost Egyptian artifact. I'm sure I have mine somewhere in some box.