You can use a rule to quickly find the center of a board's width without dealing with small fractions. Lay the rule across the width, keeping the scale's zero mark lined up with one side. Then angle the rule so that an even number lines up with the opposite side. Mark the board at half the distance. You can also find the center by drawing an "X" diagonally across from one set of opposite corners, then across from the other set of opposite corners. The exact center will be where the lines cross.
When you’re choosing a water heater, don’t be tempted to simply buy the lowest-cost model available. Water heating uses too much energy to make the decision lightly. The unit’s initial cost is a small fraction of the money that will be spent operating it over its lifetime.