Learning ResourcesPrecision School Balance, Includes Weights

Recently I decided that I needed a decent but inexpensive balance. This need arose when I decided to correct the micronutrient deficiencies in my lawn. I calculated the small quantities that I needed for the compounds with the needed elements (B, Cu, and Zn), and I ordered them. But I didn't have any way to weigh out the precise quantities that I needed to apply.I hoped that I would find a decent inexpensive balance for maybe less than $50, but I didn’t really have a good sense of what it would cost. I discovered that there are many electronic “scales” for kitchen use. They all require batteries, and I wasn’t fond of the idea of another gadget that needed a battery. And even though the precision of these scales is evident in the number of decimal digits in the display, accuracy is not always equal to precision. I decided that I wanted a balance.I was surprised that I could not find many balances that were intended for real work as opposed to a learning tool for children to play with. The few professional balances that I was able to find were considerably more expensive than what I wanted to spend. When I looked more closely at the balances intended for use as educational tools for children, the Learning Resources Precision School Balance stood out as a balance that would potentially be usable for real work. And the cost made it especially desirable, if in fact it proved to be useful for the kind of real work I needed to do. There were several reasons that it gave me the sense that it might be useful for real work. The cups, which are large and square, rest on self-leveling platforms, without any hangers that would always be in the way. It also looked like it might stand up well to moderately rough handling.When it arrived, I was pleased to discover that it met all of my expectations. It is exactly what I needed, and I was especially happy with the fact that something like this even exists, that can be used for real work and that costs less than $50.On the front of the retail box, it reads, “2000 g capacity with .5 g accuracy”. Even though the heaviest thing I weighed was 50 gram, I have no doubt that it is able to support 2.0 kg as claimed without damage. (2.0 Kg is equivalent to 4.4 lb.) Although, if you add up all the weights that are included, the sum is 106 g (.23 lb). If you want to weigh anything heavier than this, you’ll need to purchase some more calibrated weights.In a pinch, you can use the included weights to measure out exact quantities of water which you can then transfer to zip-lock plastic bags. You can easily make yourself several 50-gram weights. Ideally, you should compensate for the weight of the plastic bag. And if you use a plastic drinking cup to hold the water while you weigh it, it is even more important to compensate for the weight of the plastic cup. Instead of doing this entirely with water, you can include any number of small heavy objects, and add only as much water as is needed. Coins work very well for this, as do marbles, etc.Accuracy for this type of balance is a question of sensitivity. This sensitivity of this balance is good enough to permit the error in a measurement to be less than +/- .5 gram. This is what the box says, but you need to be good with this kind of thing in order for the error to be less than 1 gram. When you make a measurement, you eventually have the two sides balanced to where one side is heavier than the other by an amount that is less than 1 gram (in which case the error is known to be not greater than +/- 1 gram). At this point you need to use the needle and scale in order to obtain a measurement where you know the error is less than some increment smaller than +/- 1 gram. This requires a scale that is marked very exactly. Ideally you would use a .5 gram weight - which is not included - and make the scale yourself. Without having a .5 gram weight, you can make the scale yourself with marks at +1 gram and -1 gram. Then you need to visually judge whether the needle has or hasn’t moved more than half way to the +1 gram mark (or the -1 gram mark) on one side. This technique is less than perfect because the correct location for the +.5 gram mark is not exactly halfway between the 0 mark and the +1 gram mark (ditto the -.5 gram mark). If you want measurements where you can say with absolute certainty that the error is less than +/- .5 gram, you need a scale with precise marks at +/- .5 gram and also at +/- 1 gram. In order to make this scale, you need a calibrated .5 gram weight.It is generally necessary to pay attention to whether the needle swings back-and-forth freely, several times at a minimum, before it comes to a full stop. If it does not do this, it means that there is some friction somewhere, interfering with the motion of the beam (the “beam” is the moving part which includes the needle and the two self-leveling platforms). With most any balance it is necessary to pay attention to this, and this quickly becomes automatic. However the need to pay attention to this is a bit greater for this balance than it is with balances intended to be used for real work. If you detect that the needle does not swing back-and-forth freely, several times at a minimum, then you need to grab the two ends of the balance gently with both hands and move it around slightly to make certain that, given the slight amount of front-to-rear play in the position of the beam, it is not positioned all the way to the front or to the rear. Additionally, you need to make certain that the beam is not turned with one end slightly to the front and the other end slightly to the back.There is a minor rub, in the literal sense. The plastic weight that slides along a rail on the back of the beam (this weight allows you to compensate for any difference in the weights of the two buckets, etc.) is able to rub slightly against the upper portion of the base. If this occurs, it will create friction that will likely be rough and uneven, such that the beam will catch and the measurement will have a slight error. This error will be very slight, likely not more than 1 gram, so this is really nothing more than the slightest of annoyances. However, if this bothers you, there is an easy way to fix this. The little plastic weight has a small rectangular hole of sorts running from side to side; the rail passes through this rectangular hole. The front-to-back dimension of the rectangular hole is slightly greater than it ideally should be, which gives the weight a slightly excess amount of front-to-back play. A simple way to correct this is by making the rail thicker by adding a piece of stiff cardboard to the backside of the rail. Or if you have some scrap aluminum sheet the right thickness, this will be better than cardboard. Or some plastic of the right thickness. Whatever material you use, the thickness of the material needs to be just right, .7 mm to .9 mm, or 1/32”. The height needs to be 10 mm to 12 mm, or .4” (13/32”). The length needs to be 10 cm or 4” minimally, however in order to ease the task of attaching this piece to the rail, the length should be about 15 cm or 6”. If the thickness is right, you should be able to just barely slide this piece of material between the weight and the rail, on the back side of the rail, thus forcing the weight fully to the rear. After precisely centering this piece of material on the rail, the best way to affix it to the rail is by using some very thin double-sided tape, e.g., carpet tape, placed under both ends. If you deem it appropriate to use glue, I discourage using super glue for something like this, because the risk is too great of gluing your fingers to each other or to something else.This will likely solve the very minor problem, but if it does not do so to your full satisfaction, you will then want to remove the two little bumps located on the front face of the little plastic weight. To remove these two little bumps without removing the weight from the rail, the best tool will be a small wood-carving chisel with a flat cutting edge. However if you add a piece of material to the back of the rail as discussed above, it should not be necessary to bother with the removal of those two little bumps.Finally, there is the matter of the scale on the front. The balance as delivered has some little marks molded into the front of the base. It did not seem to me that these little marks were usefully located. As discussed previously, the marks need to correspond exactly to +/- .5 gram and +/- 1 gram weight difference between the two sides. To make it so, you have to stick a piece of white cardboard under the needle and mark the scale yourself. You ideally need to use a calibrated .5 gram weight to do this. You first use the calibration weight to get the needle perfectly vertical, then place the .5 gram weight on one side, mark the location of the needle, do the same for the other side, then repeat this using the 1 gram weight. If you really need measurements that are accurate to .5 gram, this is how you do that.

I'm a homeschool mom and I've been unhappy with every other classroom scale I've seen or purchased. They all seem so flimsy and inaccurate and has been frustrating instead of helpful in school - I thought I was going to have to spend big money in order to get one that would work for us and I tried this one as a last resort - - - - IT IS PERFECT! We got it in the mail and my kids played with it for **3 hours** before I even got a chance to put it away. Every time I get it out, my kids get excited - the little weights are amazing and it seems like it will last a long time.If you want a great and affordable classroom scale, look no further. THIS IS IT!

Box clearly states that it is a 13 piece set (colored blocks not included). I only received the scale and the 2 grey tubs/ holders that go on top. The weights are no where to be found. 🤷‍♀️That means I received 3 parts of this set and am missing the other 10. Very disappointed. My kids were really looking forward to getting this scale.Update:So Amazon replaced this product and it took no time at all to receive the replacement. In fact I was shocked at how easy it was to return the item. (I usually don’t return things because of the hassle). I am revising my review because I have a good product that does what it is suppose to in our homeschool classroom.

We like the sturdiness, the fact it came with a set of weights and the trays are large easily washable and can be used to weight liquids. Good addition to our homeschooling supplies! My 7 yo loves it.

Grandson loved it

Excellent tool for elementary math and science. It seems accurate, but needs leveling each time we pull it out (Honestly, though, my house is nearly 100 years old, so none of my surfaces are level.). The front of the scale is a bit hard to read, and I'm a little frustrated that the box that holds the weights doesn't latch. We've already lost one when it got knocked off of the shelf.Regardless of these small issues, it's been great for our homeschooling purposes. I plan on purchasing a second set of weights for it.

It's pretty decent. I mean, it weighs things. But when you think about it - it's just a bunch of plastic assembled into a scale. $35 just seems a bit excessive for what it is. $19 I could see... but $35? Nah!On the whole it's pretty good and works as advertised. It does have one major design flaw in my opinion though. It has an area where you can store the weights. However, it would have been much better if you could lift that whole piece off and store it somewhere else separate from the scale. We made a rule that our boy could only use the scale if I or his mom were with him. Because he had already shown a tendency to take the weights and scatter them all about the room and lose them.But he was so absolutely captivated by the scale that he couldn't resist the the temptation to play with it. And even though I had put it high up on top of a tall chest, he managed to climb up there in our absence and take every single one of the weights and promptly lose them!So, now the $35 scale is pretty much worthless to us... after just 3 days. And this could have been easily rectified if the storage area was detachable and we could have really put it in a place he couldn't get to. But the scale is too large to hide the hole thing in a random drawer, so we had to leave it out where he could easily see it. If that piece had been detachable we would have just hid it and not minded if he played with the scale - as long as he couldn't get to the weights.