I remember the first time I had access to a scientific notation calculator
It had nixie tubes, and was the size of a typewriter, but I spent a lot of time figuring out things like how many hydrogen atoms it would take to reach the Moon.
Another time I back-calculated what the density of Brumblium (from the "Mushroom Planet" books) would have to be for a planetoid the size of Basidium to have a 1-G gravity field.
Did I tell you about drawing up a complete set of floor plans for the starship "Enterprise" (long before the commercial floor plans came out). Mine were better.
Thinking is fun!