11. Create a scale for your model thermometer. Divide the distance between the two marks into 5-mm intervals. Starting with the lowest point, label the intervals on the straw 0, 1, 2, 3, and so on. Describe your scale below.

You must have made marks at two different known temperatures, low and high
Label low 0 label high something then every 5 mm make a mark label them 1, 2 ,3, etc until you reach high. The high is at 78 degrees F and low was at 61 degrees F then the range was 90 - 32 = 58 degrees F then how many 5 mm intervals call the 5 mm n in the scale the scale would be 58 degrees F/n.

12. Measure the temperature of two unknown samples with your thermometer.

13. Record both temperatures using the scale on the straw.

I don't understand what to do for 12 and 13
Please help also this is the Build Your Own Thermometer project