The Chris's error is that he does not consider he can not draw the upper oblique line crosses trough the end the of the arc.
To coorect that, Chris must to draw the upper line crosses trough the center of the arc. In this way he is going to obtain a exact copy of angle ∠T.
By taking into account the previous specifications you obtain the following draw of the angle:
As you can notice, it is necessary that the upper line crosses trough the center of the arc.
