joint.all.js
function(dx, dy, ref) {
            // Revert the translation and measure the change in angle around x-axis.
            return point(this).offset(-dx, -dy).theta(ref) - this.theta(ref);
        }
function(dx, dy, ref) {
            // Revert the translation and measure the change in angle around x-axis.
            return point(this).offset(-dx, -dy).theta(ref) - this.theta(ref);
        }
Returns change in angle from my previous position (-dx, -dy) to my new position relative to ref point.