To determine the NIR-250 fire control radar expected target acquisition range, the following calculations were made:
- time for target acquisition: Ta < 20sec (less than 20 sec)
- time for missile launch decision and execution: Tl = 3sec
- time for missile flying to the maximum range (40km): Tm = 47sec
- expected target maximum speed Vt = 0.3km/s (Mach0.9)
- required maximum target detection distance: D = 40km + Vt * (Ta + Tl + Tm) = 40 + 0.3 * (70) = 61km

Detecting a target flying only at 60m altitude from 61km, is limited by the radar horizon.
KB1 (Design Bureau No1) used the following equation to calculate the radar horizon of the 4cm wavelength:
D=4.15*(SQR(Hr) + SQR(Ht))
Hr - altitude of the fire control radar in meters
Ht - altitude of the target in meters
D - target detection range in kilometers, limited by the radar horizon

By rearranging the equation, the required elevation of the fire control radar can be calculated: Hr = ( (D / 4.15) - SQR(Ht) ) ^2 where...
- required maximum target detection distance: D = 60km (less than 61km)
- target flying altitude: Ht = 60m
- required elevation of the fire control radar above ground level:
Hr = ( ( 60 / 4.15) - SQR(60) ) ^2 = 45m (!!!)