The Compass is an unique artifact that appears in S.T.A.L.K.E.R.: Clear Sky and S.T.A.L.K.E.R.: Call of Pripyat.
"A rare artifact – it's been several years since one was found. The artifact can locate gaps in anomaly fields, effectively acting as a compass. It is believed that it can help one traverse the most complex anomaly fields completely unharmed. However, very few know how to handle it properly." - Call of Pripyat in-game description.
Clear Sky Description. The Compass gives a +6 in endurance, just like the Snowflake, although without having any downside, making the artifact very effective.
Call of Pripyat Description. The Compass combines the effects of a Crystal, Stone Blood, Sparkler, Battery and Stone Flower into a single +4 radiation artifact. The bonus granted by the Compass is overall poor, however considering it combines the effect of five artifacts (five slots are available to some suits after upgrades, but there will be no room left for anti-radiation artifacts) weighing 2.5kg together, while the Compass weighs only 0.5kg, it is a good combination. Generally speaking, the Compass is best paired with a suit with fair anomaly protection, as the extra protection given by a Compass is barely helpful to increase the protection of combat-oriented suits such as the PSZ-9d Duty armor.