it is a value assigned to the config file depending on what you select in il2setup under videp card option - full details in my guide at aiwarfare

0 - Safe Settings
1 - Default Settings
2 - Maximum Settings
3 - NVidia GeForce 6800/6600/FX/4/3
4 - NVidia GeForce 5200..5900 - 1.x Shaders
5 - NVidia GeForce 4MX
6 - NVidia GeForce 2 GTS/MX/256
7 - NVidia Riva TNT2
8 - ATI Radeon X800/9800/9700/9600/9500
9 - ATI Radeon 8500/9000
10 - ATI Radeon
11 - Intel 915/925 (GMA900)
12 - Kyro II
13 - Matrox G400
14 - 3dfx Voodoo 3
15 - 3dfx Voodoo 5
16 - S3 Savage 4
17 – Custom