blood compass 

Especially useful for adrenaline junkies, and those who love all things to do with the great outdoors. If some crazy maneuver, jackassesque like stunt, hard fall, or animal attack results in blood you now know you should adjust, prepare or tweak your attempt #2 (or #3-100) accordingly. Hence the event that rocked you to the point of bleeding has become your blood compass.

"Damn! Did you see how bad Gavin road-rashed his face after attempting that small-margin-for-error landing from skydiving with skis on?"

"Yeah, he got fahked up! That move is definitely his new blood compass now."

blood compass by swissmisz September 12, 2014

Blood compass 

Used in video games, a 'blood compass' shows which direction you've taken damage from. Some blood compasses also show how high or low the damage is coming from.

When I took damage, I could see where the enemy was, as my blood compass was pointing in their direction.

Blood compass by ahelpfulstranger June 26, 2017