Saturday, November 19, 2005

One more parent conference story...

This one I totally forgot until this morning, when I suddenly recovered a memory.

What would YOU do in this situation?

I'm meeting with the father of a nice but slightly-below-average sixth grader. I tell him that her lowest grade was on the quiz on measurement. I explain that it was a very hard quiz, because I required them to be very precise. I make a little joke about driving over the bridges these kids might build some day, and the need for exact measurements. He says he completely understands, because he works in construction or some such thing and they have to measure all the time, and if they are only a little bit off it could cause major problems.

So far so good.

Then he says, well, she probably had trouble because when measuring in centimeters you start at the zero but when measuring in inches you start at the one, and it's easy to think you should start at the zero line, in fact, he's always having to correct the young guys at work when they start measuring from the zero for inches.

And then he starts demonstrating with his hands holding an imaginary ruler and it's clear that he really means what I think he means. And suddenly I want to go back to his daughter's quiz and see if she was one inch off on all her measurements.

I smile weakly and try to get us past this part of the conversation as quickly as possible. Now is not the time for me to suggest to this man who is obviously hardworking and proud of his skill that he has been measuring wrong for his entire career, nor do I think that a five minute parent-teacher conference is likely to cause that kind of paradigm shift even if I tried to correct him. But I am certainly not going to say anything to suggest agreement, either. And I have a new understanding of why building projects end up going way over budget, given the number of boards they must cut that are one inch too short....



Blogger your math teacher said...

Is he from this country?!? Perhaps he is confused because he has been using the metric system all his life. Who knows..

Sigh. Maybe we need to start putting instructions on american rulers. I just noticed that my cheapo 6" ruler doesn't show a zero mark for either cm or inches, yet my fancier angle ruler clearly shows zero markings for both. Maybe that is why this man is confused. He probably thinks that a ruler with no zero marking means he should start measuring from one.

1:13 AM  
Anonymous Anonymous said...

The father is correct, if unclear. On construction sites 1 foot is usually measured as 1" - 13", not 0" - 12" on tape measures. I am aware of two reasons for this:

1) The hook is not precisely attached. Take out your tape measure (not ruler - they're (almost) never used on construction sites for obvious reasons). Use the hook and measure to the 12" mark. Measure again with a decent ruler. If the tape measure's 12" mark is within 1/16", then you got lucky; the hook usually isn't that precise.

2) Construction tape measures are used extensively. Your tape measure is probably used less in a year than a construction tape measure is used in an hour. The hook is frequently used to pull the tape, resulting in significant wear to the tape itself and the rivets securing the hook. It is not uncommon for this to end with the hook falling off and the tape left inaccessible inside the housing. Over the lifespan of a tape measure this wear can cause the 12" mark to move 1/4" relative to the hook.

The 1" mark is used instead of 0" (as opposed to the hook) on tape measures because there's often not a usable 0" mark on tape measures (the rivets and hook often obscure any markings under 1"). This also reduces the temptation to use the hook because it's quicker.

12:09 PM  
Blogger ms. frizzle said...

Wow, fascinating. But you do see how this could confuse a kid!

1:17 PM  
Anonymous Anonymous said...

Did you notice if the answers were off by an inch?

Review her answers. If she did measure from the 1, explain that rule is used in construction for the reasons stated above, but for the purpose of the test, we use the zero.

Then give her the credit because she may have been tutored by her dad.

Do you guys use a rubric where the solution may be wrong, but give credit if the stategy is correct?
That would bring her grade on a 1-4 rubric as a high 2 which is approaching the standards.

3:11 PM  
Blogger your math teacher said...

I still don't understand something. If measuring from zero inches is inaccurate because of the hook, why doesn't the same problem occur when measuring from zero in centimeters?

10:14 PM  
Blogger bev said...

J - because in the US, very little construction is done in metric. I'd say probably none. So the parent had really never measured in centimeters for construction. He probably thought he was just somehow being polite to the misled Ms. F! ;-)

Plus, to add to the confusion, if he's doing framing, his tape measure is probably marked somehow every 16" so that he can set up studs to be 16" on-center. And he again might start with the first 16" mark because of how inaccurate his tape is.

Having said all this, my husband is an ex-engineer (of the electrical sort) turned contractor and while he likely does measure from the 1" mark because of inaccuracy of his tape measure - I've done it as well when I help him - he knows better than to say that you *always* start at 1" for inches.

12:26 PM  
Blogger KC said...

OK, so I'm a day late and and inch short, but...

It's true that contractors and a lot of other trades will measure from the 1 (or some other mark that makes sense given the geometry of what you're measuring and what you're measuring with) -- but you also have to know why you do that, and know to offset by that 1 or else. If you need to measure 6" and you start from the 1" to get an accurate start point, you'd better know you're looking for the 7" measure or else...

So the dad's confusion is just that, confusion.

4:06 AM  

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