measuring

I am measuring 10 cm along the bottom of this board.

I am now measuring another 10 cm from my last measurement

I am doing it for the 3rd time

4th time...

5th time

lots more...

13th time

...14th time...

15th and last - at last!

As I measured 10cm 15 times, I should have 150 cms marked out in all.

So how come I have 153.9 cms?

Going to have another go with the steel rule -10cms...

150 cms...

Now to check with the tape..

Er... This time I am 4mm too short.

Dad says that is unbelievably good!

Errr....

I thought he would think that was bad!

He gave me another word.

Tolerance.

Er....

Dad said...

If I have a piece of 2x4 timber and I ask you to cut me off a 1 ft length of it..

Would I be upset if the piece you cut off is 16 inches and cut off all crooked?

I said....Er.....Yes!

Why?

Er... because it wouldnt be what you asked for?

Supposing I wanted the pice of wood to stop the trailer running into the bins again...

Would 16 inches be as good as 12? In fact, if you turned up with a brick, would that do?

Er...Yes. Anything would stop it, so it would be as good.

So I would "Tolerate" anything from about 6 inches up to about 20 in this case, and I dont even care if its not wood.

Next one.

If you build the bottom of your boat 18 ft long, and build the sides, 18ft 3 inches long, would that be ok?

Er....Would it leave a gap? Could I fill it?

Not in this case. You would have to try sailing it with a huge hole, which would let in lots of water.

Would you tolerate that?

NO!

When you measure anything, your measurement will not be exactly right. Every time you measure you will gain or lose a bit. That is why your 10cm measurements did not add up to 150cm.

However, when you measured the 150 from the end of the board in one go with the tape, you were as accurate as on each of the other measurements individually.

So....

When marking out your wood, you need to measure each line from one end and one side with a tape as that is the most accurate way of doing it.

So now I have a job for you......

Convert all your drawing dimensions into cms by multiplying by 2.54, then calculate all the measurements from one end and one side.

Then you can start building it!

Ive got a drawing done and ready to go!

Yess!