# Polarity of a relative angle - Knee joint angle

I'm wondering if it's correct to write:

$$\alpha = \theta_{lg} - \theta_{th}$$

EDIT: the theta angles are defined positive in counter-clock direcction, instead alpha in clockwise direction. My goal is to find a relationship between the three angles I wrote above (the relationship should be valid at any time istant).

$$\alpha = suplement(\theta_K )$$

therefore,

$$\alpha = 180- (\theta_K) = 180-(\theta_{th}- \theta{lg} )=180 +\theta_{lg} -\theta_{th}$$