In SH4 you can also set manually the wished heigth in the circular dial by dragging the transparent triangle and not use the recognition manual at all. I do it a lot to estimate distance based on funnels, bridge and kingposts instead of using mast
The heigth of those parts I calculate using rules of thumb: 8 feet for each deck, then use the decks as yardstick to approach the bridge or funnel heigth. Works usually well
