Squats
Forward Observer 10 cm 6+ 0 Bolt Pistol 25 cm 1 5+ 0 HQ, Special
Stand + Rhino 100 pts

Imperial Guard
Forward Observer 10 cm - +2 Bolt Pistol 25 cm 1 5+ 0 HQ, Stealth, Special
2 Stands + Rhino 100 pts

Adeptus Mechanicus
Forward Observer 10 cm - 0 Bolt Pistol 25 cm 1 5+ 0 HQ, Stealth, Special
2 Stands + Rhino 50 Pts

Elysian
Forward Observer 10 cm - +2 Bolt Pistol 25 cm 1 5+ 0 HQ, Stealth, Special
2 Observer stands + Rhino 100 Pts

Eldar
Forward Observer 10 cm - +0 Shuriken Pistol 25 cm 1 5+ 0 HQ, Stealth, Special
Forward Observer stand + Command Falcon Stand 150 Pts

Marines
Forward Observer 10 cm 5+ +2 Bolt Pistol 25 cm 1 5+ 0 HQ, Stealth, Special
Forward Observer stand + Command Rhino Stand 50 Pts

Chaos
Forward Observer 10 cm 6+ +2 Bolt Pistols 25 cm 1 5+ 0 HQ, Stealth, Forward Observer
Forward Observer stand and Rhino 100

Special Ability: Forward Observer
While any unit may call in an indirect barrage, many armies
have specially trained and equipped spotters. These troops are capable
of relaying precise coordinates and deciding on the appropriate
ammunition to use. Any barrage directed by a Forward Observer will
scatter 1D6 cm (instead of 2D6). All FO units are HQ units and have
the Stealth ability.
FOs are also the only units capable of calling in an Off-Board
Barrage. A single FO stand may call in any number of indirect barrages
against any number of targets, or a single Off-Board Barrage. FOs may
not request fire if they are involved in Close Combat, and may not both
call in fire and shoot.
To call in an Off-Board barrage, the FO must make a communications
roll of 3+ on a D6. If the roll is successful then the barrage
arrives anywhere in the FO’s line of sight. Failure indicates the spotter
has given the battery the wrong coordinates, or the battery is preoccupied
with other things. Multiple Off-Board Barrages do not combine fire
– they are resolved separately (including separate scatter rolls), even
if they are called in on the same target by different stands belonging to
the same Forward Observer Team.

Why's the Eldar one such a pussy, wouldn't he have Ranger training and such?

Chaos SM and Chaos Cultist should be separate. CSM should be a Vet with Vet stats

Forward Observer: Both speed and accuracy are vital when calling for artillery support, and the Imperium has
expertly trained Forward Observers to aid their artillery batteries. They are HQ units and have the Stealth ability.

I'm sure he'd say they are very well trained and normally a small unit.

Well, IIRC in Desert Storm they used SAS behind enemy lines before the kick off to spot for Artillery and air strikes.

Well, to be honest I rarely use FOs. For 100 points you get a unit that only slightly enhances your artillery fire (only one d6 scatter sounds better than it is, and the unit normally cannot see the important targets anyway). On top of that, in most of my games they were charged in the first or second turn. I think they are ok as they are. Should they only be able to spot one target per turn they would become pretty useless. Don't forget that even in an unguided indirect fire you will get a 1/3 third chance to be on target.

I rarely use FOs