American Action Fund for Blind Children and Adults
Future Reflections
Special Issue: Science, Technology, Engineering, and Mathematics (STEM)       WAYS AND MEANS

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## High-Caliber Challenge, Low-Tech Solution

by Cricket Bidleman, Dan Brown, and Mike Tomac

From the Editor: The challenges of helping a blind student participate fully in the laboratory may seem daunting. However, with determination and creativity, low-tech solutions sometimes can be found. In this article, a high school physics student and her teachers describe their invention of a simple tactile device for making accurate measurements to the hundredth of a centimeter. Cricket Bidleman is a high school junior in Morro Bay, California. Dan Brown worked with Cricket as a student teacher, and Mike Tomac is her teacher of AP physics.  They wrote an earlier version of this article for publication in The Physics Teacher magazine. Their piece appeared in the May 2016 issue.

From the outset, we realized that our new student, Cricket, would be at a severe disadvantage in the physics laboratory. Blind since birth, she would be unable to make the measurements needed to get much meaningful lab data. All of the sighted students could use high-level vernier calipers. For Cricket, our only equipment was a plastic centimeter ruler with tactile divisions to the nearest centimeter, a gadget we had acquired on loan. For work in a scientific laboratory, this was of course unacceptable. There had to be a way to solve this problem.

Using the vernier scale concept, we decided to make a low-tech tactile caliper. The new caliper would ultimately end up having close to 100 times greater resolution than the plastic centimeter ruler, and it could be used quickly and easily by a totally blind student.

We used the tactile centimeter ruler as a fixed scale and clamped it onto the lab table. Then we clamped a scrap piece of doorstop molding at a perpendicular against the left end of the tactile fixed scale to serve as a stop. We used a carpenter’s square to make sure the two stayed perpendicular. Another piece of scrap molding served as a sliding vernier scale that would slide along the top edge of the ruler.

Using a wood burner, we carefully made ten tactile divisions in the wooden slider so that it matched up with nine of the centimeter divisions on the plastic fixed scale. The result, according to the theory of how a vernier scale works, would at this point give 10 times more resolution than the tactile centimeter ruler.

Cricket was a great help here. She enthusiastically placed an aluminum cube onto the centimeter ruler against the perpendicular stop. After feeling where the cube was on the ruler, she concluded that the cube was a tiny bit more than 3 centimeters in length. She then slid the tactile vernier slider against the cube. She felt the tactile divisions on the slider and found that the first division on the vernier slider happened to be the closest mark to match with any mark on the centimeter ruler. From this, she concluded that the cube was about 3.1 cm. To our amazement, her results compared favorably with student teacher Dan Brown’s measurements with a commercially made vernier caliper.

Inspired, we then decided we wanted more. We immediately attempted to make a second sliding vernier scale that would give us even greater resolution. We obtained another strip of scrap wood and used the wood burner to make ten divisions that would, in this case, match up with nine divisions of the first wooden slider, not with the centimeter ruler.

With the new device, any measurement would require two steps. In the first step, Cricket would place the item on the centimeter ruler and push the first slider against it. Then she would feel the tactile divisions of the first slider against the centimeter ruler’s divisions to get a first approximation to the tenths place.

The object would then be removed, and the first slider would be moved all the way to the stop. The object to be measured would then be placed along the top edge of the first slider between the second slider and the stop. Cricket would then feel which division on the second slider matched up with a mark on the first slider directly below it.

In the case of the aluminum cube Cricket measured, the fifth mark on the second slider was the closest match. This meant that this more accurate reading was 5 hundredth of a centimeter more than her earlier approximation of 3.1 cm, giving a final total measurement of 3.15 cm. Again we compared Cricket’s reading with the commercially made vernier caliper and again the results were in excellent agreement.

Here is a table showing a brief comparison between more of Cricket’s readings taken of different samples and our readings using a commercial Vernier caliper:

 Wooden Tactile Device 1.91 cm 4.83 cm 1.24 cm 4.96 cm Commercial Vernier Caliper 1.91 cm 4.84 cm 1.27 cm 5.00 cm

Not surprisingly, some of the measurements didn’t quite match up.  Why?  We found that some of the tactile divisions on the plastic centimeter ruler were slightly greater than one centimeter. It would not be difficult to make improvements on the device. Given more time, we could make the wood-burned divisions in the sliders more accurate, too.  Those who have access to basic machine shop tools could easily make the tactile sliders from aluminum bar stock, making them extremely accurate.

When some of our sighted students saw Cricket using this homemade device, they wanted to try it for themselves. Some of them found that it was easier to use than the standard vernier calipers, which have such tiny divisions that they are difficult for most people to see. Maybe we’re onto something that could benefit all lab and shop students, both sighted and blind.

We invite you to make your own vernier tactile measuring tool. Maybe you can even make one that will measure to the ten-thousandth’s place, using four sliders.

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