Attach a scale to the wiper arm where the wiper blade attaches.
Measure the force required to lift the wiper arm perpendicular to the windshield
to normal working height (the height with the wiper blade attached).
Replace the wiper blade element if the rubber element which contacts
the glass is not on the centerline of the wiper blade +/- 15 degrees.
Refer to
Wiper Blade Element Replacement
.