Texas Instruments TI-55-II Scientific Calculator. Programmable!

“With 112 powerful functions for professional engineering, science, and math applications…Use up to 8 memories.“

which should make calculations easier than using ye ol’ slide rule.

I don’t think the quick reference guide below is the Sourcebook, but it does have basic explanations. “Comes with the revised and expanded edition of Calculator Decision-Making Sourcebook that shows how to use all its power.”

For more than you would ever need to know, there are several vintage calculators museum.

Status: The sea monster is growling that this needs to be opened and pulled apart for parts. She is hungry.