One of the most common questions that we get is "Why does the range value increase/decrease at odd increments when adjusting the target size or subtension?". The short answer is that the the application is set to "Subtension Input" by default and the range value is derived from the physical size of the target and how larger the target appears in your reticle (subtension). If you want to dial in a specific range in Yards or Meters, tap the Settings button, and change the Mode value from Subtension Input to Range Input.
Mil-Dot Ballistics provides two different ways to input the range to your target.
- Range Input
This mode allows you to enter the range to the target directly in Yards or Meters. This is the preferred mode of input if you have known distance targets, or are using another method of range estimation (i.e. laser rangefinder) and want to get a ballistic solution for that range.
- Subtension Input
This mode allows you to estimate the range to a target at a unknown distance by inputing the physical size of the target along with the subtension of the target. The formula used to estimate the range is:
(Size Of Target In Yards * 1000)/Mils = Range In Yards or (Size Of Target In Meters * 1000)/Mils = Range In Meters
The amount of jump in the range estimation when changing the subtension value will increase as the target size increases and the subtension value decreases.
To illustrate this, we'll start off with a target that's 36" (1 yard) tall that subtends 5 mils in the reticle.
(1 Yard * 1000)/5 = 200 yards
Now lets say the same target subtends 5.025 mils in the reticle.
(1 Yard * 1000)/5.025 = 199 yards
That's only a difference of 1 yard for a 0.025 yard change, so it's pretty easy to get a fairly accurate read on a 36" target at 200 yards. The but as the subtension value decreases, it becomes more and more critical that you subtension reads are as accurate as possible.
Now, if you have the same 36" target (1 Yard) that subtends 1 Mil in the reticle, the formula looks like this
(1 yard * 1000)/1 Mil = 1000 yards
And if we change the value of the subtension to 1.025 Mils in the reticle, the formula looks like this:
(1 yard * 1000)/1.025 = 975.6 yards
Thats a difference of 24.4 yards with a subtension change of only 0.025 Mils!