The importance of the hypotenuse

— post by Jesse Tune, Project Co-Director

 

Today is the day that many people have been waiting on – the start of actual excavations! The students were split into two crews: one crew of students worked on finishing up shovel tests in Area I, while the other crew headed back to Area A to setup the excavation grid and begin excavations.

The preliminary results of the geophysical survey in allow us to make an informed decision about exactly where in Area A we want to excavate. As a result, we need to carefully lay out the excavation grid exactly the same as the grid used for the geophysical survey. We also must take extra care to ensure that each 2 meter x 2 meter (6.56 ft. x 6.56 ft.) unit within the grid is a perfect square. It is important that each unit is exactly 2 meters x 2 meters so we can precisely document where every artifact and evidence of human activity is located. This process consists of using several long reel-tapes, countless pin flags, a bit of patience, and a little basic trigonometry.

We start by using two tape measures to establish a south and east baseline. Two additional tape measures are then used to mark the west and north lines of the grid and create an 18 meter x 32 meter (59 ft. x 105 ft.) rectangle. However, simply because opposite sides of the rectangle are the same length does not mean that the excavation grid is set up with 2 x 2 meter square units. A diamond has opposite sides of equal length, but they do not meet in 90 degree corners; thus, not squared. This is where a little trigonometry comes in handy. Thanks to Pythagoras of Samos, we can quickly and easily determine if the corners of our grid are 90 degree angles, and thus if our grid is set up correctly.

Grid 1

The only time they are allowed to sit while working! Field school students (L to R: Nathan, Susan, Kelsey) hold down reel tapes and prepare pin flags for the excavation grid.

 

The Pythagorean Theorem says that A2 + B2 = C2, or essentially that if we add the square roots of two sides of a right triangle together, it will equal the square root of the hypotenuse. So we know that the distance between two opposite corners of our 18×32 meter grid should be exactly 36.715 meters.  By using Pythagoras’s simple equation to ensure that our grid is perfectly squared.

A perfectly square 2 meter x 2 meter unit. The orange pin flags mark the corners, the pink string outlines what will be the outside walls of this unit.

A perfectly square 2 meter x 2 meter unit. The orange pin flags mark the corners, the pink string outlines what will be the outside walls of this unit.

We are off to a great start to excavations and already have four 2 m x 2 m units down 10 centimeters (cm) (approx. 4 inches ) or more in depth. We should have at least a total of seven units in active excavation by Friday.

Three of the four 2 meter x 2 meter units in active excavation.

Three of the four 2 meter x 2 meter units in active excavation.

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s