Mil dots a linear function?

S

Scott Bear

Regular
Rating - 100%
86   0   1
Location
Prince George
I have been looking into the geometry of how mil dots are calculated. I graphed how many mils a 12" target would be from 100 to 1000 yards and was surprised to see that function was not linear. I know the tan function is not linear, but the angle doesn't change so that shouldn't be an issue.

Is the same object at different distance perceived by our eyes and brain not linear? I don't really want to break out the old Physics and Biology text books (and possibly psychology). What am I missing?

I'm sure I'll answer the question myself in the next couple of hours, but some other insight would be helpful.

SB.
 
Angular measurement. 1 Mil is 1meter square at 1000 meters......so 0.1 increments are 10cm at 1000M. 1mil is thus 10cm at 100m. 1 mil at 100yards works out to 3.6".



.
 
A straight line is a straight line and if you keep the root angle the same, the subtension stays consistent.

With a scope, you have so much error that subtension at long range is really an approximation. For its original intent, close enough was good enough.

If you are trying to drop a bullet on a small object at LR and using a scope to range, the odds of getting a precise measurement is not all that great unless you have very good glass and alot of practise.

There is a reason why laser rangefinders are now SOP for anyone serious about LR shooting.

Jerry
 
So, am I correct in assuming you are referring to the linear increments in mils not correlating to a linear increase in yardage distance when using a 12" target?

12*27.77/.1 mils=3332 yds.................12" .1 mils 3332yds
12*27.77/.2 mils=1666 yds.................12" .2 mils 1666yds
12*27.77/.3 mils=1111 yds.................12" .3 mils 1111yds

Sort of like the above example?
 
If you graph the mills a 12" target takes up at various ranges. I thought it would be linear.

Yards Mils
100 3.33
200 1.67
300 1.11
400 0.83
500 0.67
600 0.56
700 0.48
800 0.42
900 0.37
1000 0.33
 
You need to look at it a little different to make it linear:
At:
100m a mil is 10cm high (1/1000 the distance)
200m a mil is 20cm high (1/1000 the distance)
300m a mil is 30cm high (1/1000 the distance)
400m a mil is 40cm high (1/1000 the distance)
500m a mil is 50cm high (1/1000 the distance)
600m a mil is 60cm high (1/1000 the distance)
700m a mil is 70cm high (1/1000 the distance)
800m a mil is 80cm high (1/1000 the distance)
900m a mil is 90cm high (1/1000 the distance)
1000m a mil is 100cm high (1/1000 the distance)

The mil (or 1000th) stays the same and the height/width it covers changes, as it is a ratio. Which is why you can use for rough range estimation - at 2X the distance a mil linearly covers twice as much. Since it is a ratio the units cancel out.
What you are doing is varying the ratio with distance so the equation becomes nonlinear.

Dan
 
Last edited:
The answer to your question is that it is a 1/x function as you've guessed. (you're looking at the bottom side of a linear relation, which is how it becomes a 1/x relationship).

What is linear is the relationship between distance, and how much width (in inches/mm/etc) a mil subtends. This is a linear relationship with distance.

You probably already know this, but it should be said anyhow: A MIL IS ALWAYS 1 PART IN 1000. (it's not a metric measurement, it's not specific to metres or centimetres, etc)

Scott Bear said:
If you graph the mills a 12" target takes up at various ranges. I thought it would be linear.

Yards Mils
100 3.33
200 1.67
300 1.11
400 0.83
500 0.67
600 0.56
700 0.48
800 0.42
900 0.37
1000 0.33
Click to expand...
 
You must log in or register to reply here.
Back
Top Bottom