This isn't a comment on the Horus Vision ASLI specifically, only on whether a rifle mounted elevation meter is needed at all.
When taking any shot there are several variables which need to be determined. I'll assume the characteristics of the ammo and rifle are known. The more important variables are:
1.Distance to the target. That can be line of sight or "map distance" but they're different.
2. Wind deflection derived from the continuous wind vector and bullet drag over the trajectory. The hard part is determining the wind vectors.
3. air density
4. elevation angle to the target
Less important (but maybe needed for very long range are cartridge temperature and azimuth.
Before buying instruments it's worth considering how much each of those affects your accuracy versus distance and what equipment is needed to measure those with the necessary accuracy.
For moderate range hunting (500 yards?) your senses and practice can be sufficient.
Laser rangefinders can easily give the distance to the target to +/- 1 yard. Maximum range is just what you want to spend on the device. Visual estimation using stadia range finders (like mil-dot) may be practical if known sized objects are in the field of view but typically have a 10% or greater error. The needed accuracy increases with more the square of the distance.
Wind speed at the shooters location can be measured with a pocket anemometer or estimated with practice by the "feel" of the wind but downrange winds are even more important than at the shooters location for shooting over about 600 yards. With lots of practice one can get fairly good at estimating wind deflection from mirage, plant movement, and windblown particles, but there are no affordable instruments which can measure wind accurately other than at the shooters position. Visual wind estimation is more difficult in mountainous terrain than on flat ground and also more difficult in low light.
Those two measurements are the most important to accurate shooting.
Air density measurement has become fairly simple to measure with electronic or mechanical devices which cost $100 to $200. But one can do a decent job of estimating air density by estimating the temperature, altitude and guessing at the barometric pressure based on the weather conditions then using a lookup table. Shooting accuracy is not as sensitive to air density as to range or wind deflection. Air density affects the drag on the bullet, but it's a secondary effect.
Likewise, most people can estimate the target elevation angle within 5 degrees with a little practice. Since the data is only useful if you've memorized multi-variable ballistics charts (or enter it manually into a computer) is a scope mounted inclinometer the best way to measure angle? I use a LTI rangefinder which gives the elevation angle with each distance reading. That seems like a more sensible place to locate the inclinometer to me. For most shooting a 5 degree estimate is sufficient for the error to be smaller than wind estimation errors. For shooting on reasonably flat land elevation angle can be ignored to around 1000 yards.
I've never considered that I need an elevation meter mounted on my rifle. If there was a "complete" scope based rangefiider that measured crosswinds downrange then the ability for the scope to also measure air density and target inclination angle would be useful for internal calculations by the scope's computer.
I'll not be buying a Horus ASLI. I do have a Horus Falcon riflescope with the H37 reticle and like it very much. It gives accurate windage and elevation holdoffs with no knob twiddling or click counting.
