Review: Distance Reduction Indicator by David Tubb

Yet another “Why didn’t I think of that?” item, the Distance Reduction Indicator (DRi) by David Tubb is a simple yet effective device for helping you make adjustments to distance for high-angle precision shooting.

I recently took a Precision Long Range 2 (High Angled Shooting) at the NRA Whittington Center, as a follow on to my class earlier this year (be on the look out for the write up on that class). One of the other students had this nifty little device that he let me borrow for the duration of the course (thanks, Matt!)


The DRi is a compact and rugged hunk of metal. It is low-profile and “constructed to withstand the rigors of field use”. It fits any standard Picatinny rail, and is level-adjustable over a 100 MOA range so you can accommodate long-range-style scope mounts. The markings are laser engraved along the side of the dial (as well as the front) meaning the data is also readable from the spotter’s perspective.

Tubbs DRi from the side.

Tubbs DRi from the side.


It is a dead simple device to use once you understand how to interpolate the data. The markings on the body immediately give you the reductions for 600 and 1200 yards. For everything else you must do some quick “in you head” math (which is much faster than figuring out the angle and doing the cosine math). They produced a video that explains it:

I used a protractor, my Leupold RX-1200i range finder, and Theodolite (an app on my iPhone; yes, I’m one of “those”) to get the angles (the class was all about Angled Precision Long Range). I then did the cosine math by hand (you know, old school pencil and paper), and used my Kestrel 5700 (with Applied Ballistics). What I found is that the estimations from the Distance Reduction Indicator were all within a few yards of the mathematical solutions from the other methods. Which in precision long range, at the distances we were shooting, was good ’nuff.

Super simple to operate. No batteries to die. No papers to blow away...

Super simple to operate. No batteries to die. No papers to blow away…

The reductions given were appropriate.


If you are into precision shooting, and you’d like to eliminate the need for using cosine calculations to correct for angles, this is definitely worth the $120.

It is super rugged and simple to use. Glance over at the Distance Reduction Indicator, find the distance marker close to your target distance, and subtract off the value. Done. Of course you still have to know your holds, but at least the angle math is handled for you.

You can find out more information at the website:,%20dri,%20angle%20cosine%20firing%20solution

Tom is a former Navy Corpsman that spent some time bumbling around the deserts of Iraq with a Marine Recon unit, kicking in tent flaps and harassing sheep. Prior to that he was a paramedic somewhere in DFW, also doing some Executive Protection work between shifts. Now that those exciting days are behind him, he has embraced his inner “Warrior Hippie” and assaults 14er in his sandals and beard, or engages in rucking adventure challenges while consuming craft beer. To fund these adventures, he writes medical software and builds websites and mobile apps. His latest venture is as one of the founders of; a search engine for all things gun related. He hopes that his posts will help you find solid gear that will survive whatever you can throw at it–he is known (in certain circles) for his curse…ahem, ability…to find the breaking point of anything.


  • bpm990d

    It’s spelled Tubb, no “s”.

    • Doc Rader

      Good catch! Should be fixed.

  • Glenn Bellamy

    Horus Vision has sold these for years.

  • Sunshine_Shooter

    That’s really smart.

  • Wolfgar

    Looks simple and very useful, great idea.

  • I was hoping this was something that would change the elevation off the scope mount, and I was all excited. Instead it’s just a little milled cheat sheet…. So unlike marked turrets or such, you still have to work it all out in your head where human error happens. 120 bucks and it might be of some help to some guys. But… if you were already serious about this sort of shooting you should already have your Dope Book and you should already have a lot of this worked out, making this widget to add on to your rifle pretty much useless.

    • Mrninjatoes

      So Mad Ogre, how do you determine your angles when shooting?

  • Martin Grønsdal

    I need this for home defence, since I may have to shoot down the stairs.

    • Blake

      Grand staircase?

    • Bob Simpson

      Will it work for a spiral staircase?

      • FarmerB

        Spiral staircase with left hand twist?

  • guest

    A cosine angle indicator does not “reduce” distance, it helps correct for just that – angle, which may be up or down, and in no way what so ever cancel out other factors like wind, coreolis, or drag.

    As far as using it in conjunction with whatever method of calculation – Stelok app does it best.

    • Bob

      “I don’t know why you want to find this Strelok fellow…”