Actually, for terrain purposes percent grade is much more typically
used. You never see a road sign telling you there is an 8 degree grade
ahead ... you'll see 14 percent instead. Percent grade is easily
measured (rise/fall over horizontal run) and easily worked with. I
could, for example, calculate in my head the volume of dirt I'd have to
remove to achieve a certain percent grade from whatever the current
grade was, but I'd need a calculator or set of trig tables to do the
same if all I knew were the angles. And in many cases, you measure
percent grade (since terrain slopes are almost never uniform) to get
average angle anyway.
For ham radio purposes it's a mixed bag. Percent grade is most easily
used for entering terrain data into HFTA, but I use the angle to
subtract from the EZNEC plots I run as an estimate of what my elevation
pattern might actually be on this very long slope I live on.
I agree that there can be confusion when people are careless or don't
know the difference, but I think both have their place. Generally
speaking, I prefer using percent grade when I actually have to
accomplish something terrain-related.
73,
Dave AB7E
.
Steve London wrote:
> I often see people throw around phrases on Towertalk, such as "my hill is a
> 10
> percent grade", or "my slope is a 10 degree grade". As I discovered in a
> wildland firefighting class, these are definitely not the same thing ! Just
> to
> clarify, so we are all on the same page:
>
> Degree grade = arctan(height/distance)
> Percent grade = (height/distance) * 100
>
> So, for example, a 45 degree grade is the same thing as a 100 percent grade.
>
> An easy-to-remember rule-of-thumb is that that the percent grade is about
> twice
> the degree grade.
>
> It boggles my mind why we risk confusion and even talk about "percent
> grades".
> Isn't that why virtually every high-school graduate took geometry so we would
> have a better way to describe an angle ?
>
> 73,
> Steve, N2IC
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