With the impending holiday of Christmas approaching, the engineer could help optimize for time efficiency and benefit-cost of the present for a person, taken here as a significant other.

For time efficiency,

Te = TC/S  + J

Where:

Te = Time efficiency in gift-buying

TC = Time until Christmas in days

S = Time spent in a store, buying a gift

J = Joy Content of gift for recipient

The Joy Content is derived by a 0 to 10 survey given to the one receiving the gift. Note that the smaller TC, in other words the shorter time to Christmas, the smaller S needs to be, meaning the time spent in the store needs shorter. The goal is to maximize the Te, spending less time in a store, and bring greater Joy to the recipient.

This is the way to approach Christmas shopping.