Slipboard

I ventured to draw back the slipboard on the roof, contrived on purpose to let in air.

Source: wiktionary

When the slipboard is let down, a quantity of barley is allowed to pass into the drum-case by means of the rollers; and it is there retained under the impetuous action of the beaters as long as the feeder-in thinks proper; and when he considers it to be sufficiently rubbed and buffetted, he suddenly pulls up the slipboard, so as to allow the whole quantity of barley to be thrown, at one dash, upon the first shaker;

Source: wiktionary

When the broods are fully hatched, the young are carried with the mother to the cribs in a yard and shed, which shuts by night and opens by day in a door of slipboard, affording air and exercise with the proper shelter.

Source: wiktionary

height is measured using a flexible steel or plastic measuring tape attached to the wall or door frame; the child stands against the tape or stadiometer with the shoes removed and the heels, lower back, and shoulders touching the wall or door frame; lower a block of wood or slipboard and make firstm contact with the child's scalp.

Source: wiktionary