Determining enthalpy of neutralization and heat capacity of calorimeter by overlying with straight lines or "eye-o-metric method" Below is a model example of how to interpret gathered data. Temperature on y-axis, time on x-axis.
We are supposed to read  (temperature change by neutralization) and  (temperature change by resistive heating - to determine heat capacity of calorimeter) by overlaying the selected area with straight lines.

What I don't get is the way the straight lines are put the way they are. Maybe the bottom one: we expect the temperature drop caused by heating the calorimeter will continue by this straight fashion so we must take it into account in subsequent temp change reading.

But what about the upper line? Why read the upper value above the graph and not on its local maximum?
Ah, I understand now. It's of analogous reason to the first case. By adding heat during a time interval we expect that some of it will be absorbed by the calorimeter.