The Berk Wheel Tray is a series of four racks created by the Berkians to test wheel quality.
Four wheels, usually wagon wheels, can be laid on the tray, with one on each of the four pillars. Glowing Algae can then be poured onto the wheels in an attempt to check for cracks.
At some point before the quest "Gobber's Wheels of Misfortune", a cart wheel sold to Tuffnut by Gobber breaks apart when used. Worried about the strength and safety of his work, as Heather's knife and Mulch's anchor had also broken that same day, Gobber asks the player for help. He suggests that they take the wheel to Heather to see if she knows what happened.
Upon talking to Heather, she suggests that the player gather Glowing Algae to test the wheel for cracks. When the player returns from gathering algae from Valka and an Injured Flightmare, Heather has put the broken wheel and three other wheels on the wheel tray. Upon pouring the algae on the wheels and lighting them with Windshear's fire, it is clear where the cracks are on the broken wheel and how they occurred, as the new metal Gobber had recently begun using was not strong enough to resist the weight of an object in use. Gobber thus collects all of the objects he made with the new metal and replaces them with objects made of his old tried-and-true materials.