Ms. Coombs tries to use Pat’s ideas and directs the students to take baby steps to construct a graph that results from adding the function y=-x and y=x².  Instead of thinking qualitatively about the magnitudes, however, Ms. Coombs chooses to estimate quantitative values.

As the class proceeds, students continue to take “baby steps” across the x-axis and estimate the specific values of the functions to find the sum of the two functions. 

The procedure of step-by-step estimations that Ms. Coombs began in the previous clip continued on for three and half minutes.  In this clip she begins to employ a form of covariational reasoning to help construct the graph of the sum of the functions.

In the after class meeting, Pat discusses with Ms. Coombs how precise numerical values are extra details.  The students can, in fact, focus on estimated magnitudes to help construct the graph of the sum.  The students could use an unmarked straightedge to do these tasks, thereby lightening the cognitive load. Pat ultimately ends up recommending that graphs without axis scales be used for the next activity.