We've measured his normal heartbeat rate already.

Not that.

I mean the person as a variable.

Umm... Ibarada-senpai,

what do you mean by controlled experiment...?

...To put it simple,

this is the objective of the experiment you're conducting now.

Will A's heart beat fast when together with B?

To find out, it is necessary to compare with the result of the 「experiment of the situation when B is not present」.

Now, let's compare with the experiment when 「A is doing nothing」.

Experiment

Controlled experiment (negative control)

A pets B's head at close range.

A does nothing.

High heartbeat rate!

This is called a negative control,

a contrastive experiment where we carry it out to compare knowing that nothing will happen.

Heart rate

Heart rate

Comparison