Eötvös effect: calculation
Equation
Calculating vertical Coriolis deflection (or the Eötvös effect) is an almost identical process to calculating for horizontal Coriolis. We will need to know:
- The latitude of our position
- Our compass bearing
- The time of flight for our bullet
cos(latitude°) * sin(azimuth°) * (Time of flight in seconds) * .072 = Vertical deflection in MRADs
Where:
- positive outputs = higher point of impact
- negative outputs = lower point of impact
Data collection
Time of flight can be found in the ATragMX under the “RC” button in the top right of the screen or derived in an online ballistics program. As the ATragMX suite is not available in situations where manual ballistics are relevant, time of flight information should be recorded prior to operation start.
Bearing can be determined by aligning the in-game compass with the target.
Map latitude in Arma 3 does not always correlate with real word locations, rather this information is manually populated by map makers and is persistent for an entire map. Latitudes for common UNITAF campaigns are listed below:
| UNITAF Campaign | Map Name | Latitude |
|---|---|---|
| Operation Black Flag | Takistan, Takistan Mountains | 35° |
| Operation Deadlock | Lingor v3.9.5 | -4° |
| Operation Everglade | Rosche, Germany (2.0) | 53° |
| Operation Everyman | Armavir | 44° |
| Operation Fault Line | Lythium | 34° |
| Operation Fulcrum | Uzbin Valley | 34° |
| Operation Guardian Angel | Island Panthera | 46° |
| Operation Hetman | Livonia | 54° |
| Operation Honeybadger | Reshmaan Province | 35° |
| Operation Polaris | Altis | 40° |
| Operaton Quantum | Kingdom of Regero | 39° |
| Operation Steadfast Resolve | G.O.S. Al Rayak | 36° |
| Operation Valiant Guardian | Beketov | 55° |
Calculation example
Sgt McShooty is deployed as an SF Spotter on a Honeybadger. He ranges his HVT at 900m, a shot that will have a time of flight of 1.8s. Needing to guarantee shot placement, he measures the target azimuth at 90°:
cos(35°) * (sin(90°) * (1.8s) * .072 = .11 MRADs
Because the output is a negative value, the bullet will impact .11 MRADs higher due to the Eötvös Effect.
Equation limitations
This equation will serve well under all conditions and the very small degree of inherent error will not impede operations in either target rich or high value target environments.
