For all of us out there that just needs to measure their rocket fuel right now and can't wait. Or if you're like me who can't imagine spending money on a sale you won't use 99.9999% of the time. Here is how you can build one using your MacGyver skills and ordinary office supplies.

Step 1: Parts List

2 sheets of paper
2 large books

Step 2: Fulcrum

Wrap the spring around your ruler 3 times. Measure out an extra 5 cm (2 inches) then cut. If you have nylon string, be sure to heat the ends so they don't fray.
Tie the too ends together to make a loop,
Center this loop at the middle of the ruler.

This point will be your fulcrum,
If you hold the string the ruler should balance and sit horizontal.
The reason you wrap the string is to keep the ruler from slipping out when it tilts.

Step 3: Building Your Stand

Partially open the binder and sit it on the desk standing up.

Bend out the paper clip, and clip it on to the top of the binder
With the paper clip bent out it should make a nice hook to attach items too.
Now hook the string onto the binder. Mess with the string until the ruler wants to be horizontal when it stops moving. (In physics we call this a stable equilibrium.)

When you find your sweet spot tape it down.

Step 4: Making Your Trays

If you have a 3hole punch, then 3 hole punch both sheets of paper. If you do not, just poke a hole with a pencil when it comes time, at the end of this step.

Fold your paper in half length wise.
Fold about a cm, or half inch one the open end.
Staple this end closed.

The side with the holes punched, that your top side,
Fold about a cm, or half inch on the bottom end,
Staple this end closed also.

Now you should have a nice pocket to put stuff in. with holes at the top end, If you don t have holes make two holes at the open end to place the string.
Be sure to use the same number of staples on both sheets of paper.

Step 5: Hanging Your Trays

Now cut about 43 cm (17 inches) of string,
Tread it through the hole on top,
Make a loop using a square knot, or whatever knot you like just make sure it doesn't untie, and you have a loop that is about 42.5 cm in circumference.

Loop and hang both "trays" at the far end of your ruler. Make sure they are equal distance apart.
When you get it tape it down.

Make sure the string hangs at a precise distance. If it doesn't you will not get a good reading.
In one of the photos the tray is hanging incorrectly, can you spot it?

Step 6: Measure

Place two large intelligent looking books under the binder to allow your scale some room to move.
And your done.

Trays like this measure unknown weight against a known weight. Most of us don't own 1, 5, or 10 gram masses. But we all have coins. And US coins have a weight tolerance to about a hundredth of a gram. Which is more than we need for this project.

US pennies are 3.1 grams, those printed after 1982 are 2.50 grams.
Quarter weighs 5.67 grams
Dime 2.27 grams
nickel 5.00 grams

Now I don't know if the mass of the other coins are date dependent, like the penny. Because of this I prefer to use pennies.

From here I'm sure you can figure out the rest, measure out your rocket fuel and mediate on your MacGyver skill. Have fun!

(I don't know why this photo is slanted, it's really a feature)

Step 7: Dig Deeper

You can get more precise readings, by using smaller string, long ruler, and making better measurements.

If you don't mind doing some math you can easily scale up this project to measure just about anything.

By using Boom stick and measuring tape, instead of a ruler, plastic store bags as your "trays",
and an unopened bottle of ketchup for your known mass(or what ever unopened condiments you prefer). Printed on the label of most foods is it's weight, just remember this is only an approximate weight.

Just move your unknown mass and your bottle of ketchup back and forth along the boom stick until you find when they balance. Then remember m1 x d1=m2 x d2 mass times distance of item 1= mass times distance of item 2

m1= mass of the unknown object
m2= mass of the bottle of ketchup
d1= distance of the unknown mass to the center string(fulcrum)
d2= distance of the bottle of ketchup to the center string(fulcrum)

This method looks like crap, but it works. I used this method to measure items I was selling on eBay.
How much does each paper tray weigh?
oh, and you can find coin weights in wikipedia! (At least for euros)
That's almost like my idea! I managed to measure weights in 10mg accuracy. I use a transparent ruler and I simply balance it on a triangular ruler (http://www.woodrow.net/oneProduct.asp?productId=38). I simply put the coin on the ruler (the ruler on my construction is horizontal) on one side and the thing I want to weigh on the other, suspended on a thin string from the edge of the office. I measured the accuracy by using the scale to measure the weight of some coins with other coins. I'll sometime make an instructable for mine too, the good thing about mine is that it doesn't use tape(exept for the cointainer of the item to be measured). Well done for your scale too! I wanted to see if someone else thought about it and posted it.
 at least there's a formula for this
I like the part about coin weights! Very informative.
Cool idea! The only problem with using packaged food for the known weight is that that should be the weight of the food not including the packaging. If You were to use the ketchup bottle then your weight would be off considerably if it was a glass bottle. It would probably work using a dry good dumped into your matching weight trays though. I'm sure this will come in handy some day!

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