Need to replace your trusty old level? You can check it for accuracy. Lay one working edge on a flat surface and check the bubble. Swap it end for end, then check the bubble again. It should be in the same position. Now try the opposite working edge. Take a reading, switch end for end, and take another reading. The bubble should be in the same position. Likewise check for plumb by holding it against a flat vertical surface.
By simply caulking, sealing, and weatherstripping around all your windows, outside doors, or where plumbing, ducting, and electrical wiring penetrate exterior walls, floors or ceilings, you can save 10 to 25 percent of your heating bill.