Whatever feels comfortable. If you weld at 200+ amp all day on shade 9 it won't damage your eyes but will strain them. Shade 13 at 20-30 amps and you won't see what you're doing. W/A
one is probably sensitivity, that should be on its highest that way the least thing will darken it, you cut back on sensitivity if your working under florencent light or out in the sun, as this darkens the helmet prior to striking the arc.
delay time is the time taken for the screen to come clear after you finish welding, that can be set to what ever suit yourself, i think im right ?