Lab Group Data: Measurement (Group 6)

Summary

For this lab, we were responsible for building a groma, a measuring device from ancient Rome that allowed for the creation of 90° angles and sight-lines for straight lines. Then, we practiced four exercises with the groma: making a “road,” an “observation zone for soothsayers,” a grid/Roman colony, and measuring the area of an irregular shape.

Building the Groma

Our groma was largely composed of PVC pieces and 3D-printed parts:

• Main unit
  • a 55″ PVC piece
  • a 3-piece PVC crossbar unit
  • a 4″ PVC piece
  • a 4-way divider
  • a 3-D printed bracket (1 top and 1 bottom)
  • 4 screws
• Top unit
  • yarn/string
  • 9 beads (prevented the yarn/string from slipping through the drilled holes)
  • 4 10″ PVC pieces
  • 4 3-D printed endcaps
• Weights
  • a steel plumb bob
  • 4 3.75″ PVC shafts
  • 8 PVC butt caps (4 with drilled holes)

The weights and lengths of our weights were as follows:

Labeled Weight	Length	Weight (in grams)
Steel Plumb Bob	4′ 5″	237
Weight A	2′	183
Weight B	4′ 3″	200
Weight C	2′ 2″	182
Weight D	4′	190

Making a Road

For our road, we chose to start from the front of Leighton and head toward Laird/the observatory. We made our initial two points with the groma by lining up two, parallel side weight with the center weight (pictured below).

In the first 5 minutes that we worked on our “road,” we managed to make a straight line that was 128 feet and 5 inches long. We noticed that, even though our side weights were different lengths, the only benefit that the longer yarn seemed to provide was that it gave the viewer more yarn to line up with the other strings (in short, more possible sight-lines).

We also wished the our groma was able to stick into the ground as it, alongside the weights themselves, tended to sway a lot in the wind, which made it difficult to determine if the line that we were creating was actually straight. It seemed that a viewer would need good eyesight for this job, though I imagine that having poles with a brighter color/one that didn’t blend in with the surrounding grass would have also helped.

We also measured the distance between each of our points, which gave us distances of: 4833

• 522″, 610″, 601″, 439″, 392″, 360″, 344″, 374″, 461″, and 730″.

Our mean distance between each point was 40′ 3.3″, and our overall distance was 402′ 8,” which took us 30 minutes to lay out.

Making an Observation Zone for Soothsayers

For this exercise, we decided to make an 8’x8′ square, starting from a center point as the readings had mentioned, before using the groma at the center point to make four lines that extended outward and whose intersection formed four 90° angles.

To do this, we found the four points that were perpendicular with one another, where two points on each side would form a line that bisected the center point. Because we had knotted our rope to have a knots with 2 feet-long increments, the rope made it easy to measure out the 4′ and 8′ sections as needed (shown below) and check our right angles as the different corners. (A measuring tape likely could have also done this, but our group had the “wheel-on-a-stick” measuring device, and it was almost impossible to maintain a straight line with no references while measuring with this tool.)

It was during this exercise that we started to feel less excited about the lab, likely because we were still heavily relying on the groma. My group mates reported feeling: “bored,” “defeated,” and having the desire to “bang [his] head against a chalkboard.”

Once we realized that we did not need to use the groma beyond the few points, our process did go much quicker. In total, it took us 13 minutes to make an 8’x8′ square, which proved to be a great size that could comfortably fit a couple people who were looking for bird-signs/getting in touch with the gods.

Making a Grid/Roman Colony

Once we learned that we could use the rope after finding the initial few points with the groma, our process went much faster. For the grid/Roman colony exercise, we decided to keep our first 8’x8′ square and create more based off of this first one. As we already had the points to go off of, each square only took 10-12 minutes to create, and I could see how this would be an even faster process if we were not accounting for the road that we were also trying to create between each square.

For the road, we decided to use one of our green poles, which we had been using when creating a straight line before it snapped apart. Luckily, the larger of these snapped sections was 5′, so we used this to mark the width of our road (as we did not have a measuring tape), and we used the the smaller one for the space between the other squares.

Measuring the Area of an Irregular Shape

Our last exercise was measuring the area of an irregular shape using the groma, “wheel-on-a-stick” measuring device, and our rope. We decided to do the observatory because we were short on time, and we ultimately were only able to (attempt to) measure out a large rectangle around it.

I am not sure to what degree the unevenness of the terrain or the amount of wind that was on that hill (or both) impacted our measuring attempts, but we ended up with a “rectangle” that had four sides of different lengths: 90′ 10″ ; 111′ ; 78′ ; 105’… At this point, our steel plumb bob had also snapped off and been lost, so we substituted this center weight for a pile of woodchips, which did not work as well.

While our measuring efforts were about entirely unsuccessful, this exercise did help us understand why it would be easier to “cut away” from a larger shape, rather than “add” area to a smaller shape based on the tools that we had. By the end, however, we were still confused about how one would keep track of the triangles that had been cut away, even with flags, as it seemed difficult to visualize – especially if you’re a Roman who didn’t have any graph paper!

Reflection

After this lab, we wished that our steel plumb bob had been longer so that it could have actually made contact with the ground. Additionally, we thought that the groma‘s base was unwieldy, especially on uneven terrain, and its instability made it necessary for one person to hold the groma straight while another person use it. Lastly, we much preferred using the rope to the groma, which makes us suspect that the Romans may have also used the groma only as often as they would have needed to, which seemed to not be that often.