Additional Math Pages & Resources

Tuesday, January 5, 2010

Measuring 101. How hard can it possibly be?

In Excel Math we teach kids about units of measure. They learn about geometric figures. It seems pretty simple to put the two together -  See the shape. Measure it.

On a Lesson Sheet it is simple. We ask How large is this rectangle?

They answer, Five units wide and three units high. Perimeter is 16 units and area is 15 square units.

But when you move this exercise to the real world, suddenly things get a lot more complicated.

Let's say we want to install some mini-blinds on a window in our room. There are lots of narrow blades, all connected together by strings. They can be tilted open and closed, or pulled up and down within the window opening. Some even can be lowered to the bottom OR pulled up to the top.

It's critical to have the correct dimensions of your window openings when you order mini-blinds. It doesn't seem hard, does it? Just measure the height and width of the opening and order the blinds. But it's done incorrectly so often that mail-order suppliers offer "I measured it wrong" liability insurance!

Here's what you are supposed to do.

1. Measure the height of the opening in 3 places across the width of the window.
2. Measure the width of the window in 3 places along the height of the window.
3. Specify the blinds you want using the smallest of the 3 dimensions in each direction.

The window might not be square. The ceiling, floor, wall trim and sills might not be horizontal. The walls might not be vertical. The window itself may be crooked in the wall. Your tape measure might slip. You might have forgotten to wear your glasses. If you have lots of windows, you might confuse the measurements when putting them onto the order form. You could read the wrong side of the tape (cm instead of inches).

When your new blinds come, you find you have problems at the top, the bottom, with the way they hang and how they pull up and down. Do you send them back, tear out the window, try to re-fabricate the trim, adjust the fit? What can you do?

The most effective solution if your measurements show your house is flaky is to give up the idea of inside mini-blinds. Put your curtains or blinds outside the window frame! That way, the fit is assured and the gaps are covered. It might not be your first choice, but it can be the best choice.

Sadly this same situation can occur with more substantial items than a mini-blind. Like the new window installed in our kitchen last year. Once they broke out the old window and put the new one in, we saw the new one was too small. Here's how it looked after it was centered and leveled in the opening. There was a lot of extra space at the top, even when lifted and leveled at the bottom.

It's true that ordering a window too large would be a bigger problem, but having this gap meant they had to cover it up with wide trim pieces. And now the glass area of our window is smaller than it needed to be. And it doesn't match the other windows.

The foreman admitted that they didn't measure correctly. He said two people should have measured each window separately and then compared their results. If the measurements didn't match, the carpenters should measure again until the dimensions match. A single estimator had measured once, subtracted an inch, and ordered a window.

I can hear him thinking, It's not my house. As long as it fits in the hole ...

On the other hand, even when it is your own house, and you do try to be precise, it's easy to read a tape measure incorrectly. If you are doing the job alone, and trying to keep the flexy tape shoved against the far side of the window, while fumbling for your glasses, while peering at the marks on the tape, while scribbling on a scrap of paper (or the wall itself) ... you can see there's good reason for that old saying, Measure Twice, Cut Once.

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