Home Forums Hunting & Shooting Ask The Gunwriters Please define subtend.

Can someone please explain this term; subtend. Thanks.

Wax eloquent ye guru's; I is kinda dumb.

Thanks again.

Tech term:

To underlie so as to enclose or surround.

Non-tech term:

Betwinx and between (as interpreted by yours truly).

Dixie-
If you''re asking questions, you're not dumb.

"Subtend" is generally Karnis says. It can have special meanings in geometry. We can do better if you give a sentence or other hint.
--Bob

In shooting sense, "subtend" is how much of the target your crosshair or sights will block at a specific distance. Heavy reticles subtend more, fine reticles subtend less.

Rangefinding scopes often use statia lines (the smaller lines above and below the crosshair) to subtend a certain distance at a specified yardage - let's say 18-inches at 100-yards.

So, if the target is also 18-inches tall and spans the distance between the statia lines you know the target is 100-yards away.

If the same target spans half the distance between the statia lines you know the target is 200-yards away.

The statia lines in this case subtend 18-inches at 100-yards, and subtend 36-inches at 200-yards.

Main Entry: sub�tend
Pronunciation: s&b-'tend
Function: transitive verb
Etymology: Latin subtendere to stretch beneath, from sub- + tendere to stretch -- more at THIN
1
a : to be opposite to and extend from one side to the other of <a hypotenuse subtends a right angle>
b : to fix the angular extent of with respect to a fixed point or object taken as the vertex <the angle subtended at the eye by an object of given width and a fixed distance away> <a central angle subtended by an arc>
c : to determine the measure of by marking off the endpoints of <a chord subtends an arc>

2
a : to underlie so as to include
b : to occupy an adjacent and usually lower position to and often so as to embrace or enclose <a bract that subtends a flower>

(American Heritage Dictionary)
_ _ _ _ _ _ _ _ _ _

IOW, "cover," as in "the 1-MOA dot reticle covers approximately one inch at a hundred yards."

.

Yep, "subtend" is the layman's slang for the technical term "cover up." <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

RSY

Ah yes, someone was paying attention in sophomore geometry, and someone was not. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

jim

Thank you all very much for the replies. I was asking in relation to understanding rifle scope reticles and mildots. I think I understand fairly plainly enough, but I actually thought it was more complicated.

I was talking to premier reticles and they said that their fine cross hair covers up 1" at 1 mile. So now I understand they could have said, subtends 1" at 1mile.

I thought it had to do with range estimating and the hypotonoose thingy stuff as in Ken's post:

a : to be opposite to and extend from one side to the other of <a hypotenuse subtends a right angle>

When reading about shooting optics and they use the term subtend, are they usually only using it in its simple-ist meaning?

I had a real hard time with math in high school, and even though I did well in geometry I have forgotten almost all of it. From time to time I will use some very basic algebra for heat transfer formulas but that is it. I probably ought to purchase a high school geometry text. I bought a used one from a local bookstore and it was at the college level and I was totally lost.

Thanks a million for the help.

Dixie,

"Subtend" is kinda on a par with "MOA" in the shooting world. MOA can be used simply to define a 100-yard group, but at the same time the math indicates the group should be twice the size at 200-yards.

Similarly, "subtend" can simply be used to select the mil-dot or crosshair you want, and at the same time provide the math constants necessary to calculate the range to the target.

DF,

What you quoted Premier as saying about the FCH covering 1" at a mile doesn't sound right. Are you sure they weren't talking about a mil, or something? Like the other posters said, MOA is proportional, so 1 MOA is about 1" at 100 yards, 2" at 200 yards, and so on. At a mile 1 MOA would subtend about 17.6 inches.

Paul

Paul,

Now I know I am somewhat dull from time to time, but I am almost certain I remember the conversation that way, he explained that the fine cross hair would cover up 1" of the target that was 1700 yards away. That sounds right doesn't it? How much would that subtend at 100 yards?

Dixie,

1/17-inch...

JOG

Thanks!

That sounds about right for a fine cross hair don't it?

Thanks for all the replies.

Dixie,

I don't know...one of the rifle loonies is going to have to jump in.

PS: In a prior post I wrote "statia" - make that "stadia". The post is too old to edit. My tinfoil hat must have come loose...

Dixie Freedon:

The term subtend, when speaking of rifle scopes, refers usually to the mil dot reticule and other types such as target scopes. It doesn't imply that a cross hair covers or obliterates the target. Rather it more specifically means that when you use a 100 yard, or meter, mil dot or cross hair the next set is at 200 yards or meters. Therefore, the 100 yard/meter mil dot "subtends" to the 200 and the 200 subtends to the 300. It is "the next set" at a greater known distance or the next dot or hair that follows the first or preceding. It gives way to the next one when you look further or your target is further.

Subtend applies to both elevation and windage. Mil dots or hash marks on a cross hair are also on the windage hairs and thus the first windage marks subtend to the next set.

Target Grid

The lower half of the reticle contains the target grid. Each horizontal line on this grid equals one mil radian. A Mil Radian is equal to exactly 10cm at 100 meters. Each hash mark on the lower duplex of the reticle subtends to � of a mil radian. The "windage" marks to the left and right of the main duplex subtend to 2 tenths of a mil radian with the larger hash marks subtending to 1 mil radian. The numerals on the right and left sides equal the number of mil radians each line represents from the zero point (or the duplex cross in the center of the reticle).

Height of item in inches x 27.8 (25.4)/Mils read = Distance to target in yards (meters).



The formula can be worked backwards in training so that if the distance to the target is known we will know what the mil reading should be. This is handy for beginners learning to read mil dots. The formula for this is:



Size of item in inches x 27.8 (25.4)/Distance in yards (meters) = Mils


Bill Tibbe