Are there any cut off values to say if it is a forward head posture or not? Or are there any grades based on the measurement to classify the degrees/ severity of forward head?
Basically, one might consider 3 phases after a normal head posture.
From a saggital perspective, Normal means that the center of the ear lines up with the center of the shoulder. Therefore, Phase 1, 2 and 3 are increasing forward head posture. Phase 1 corresponds of a center of the ear lining up with the medial anterior face of the clavicle. Phase 2 when the ear lines up with the sternum and phase 3 when the ear lines up outside the tronc. See for a picture describing these postures usable on a digital photograph (http://www.chiro.org/LINKS/Forward_Head_Posture.shtml)
There are many body charts that come with plum lines. We have the patient stand next to the chart and photograph them on their own phones.Then they can follow their own progress and we can measure the degree of FHC on the chart and record it.