John, a graduate student in US, walks into his apartment kitchen with his laptop. On the counter his roommate has left a note next to what looked like a door lock. The lock was a rectangular prism with a normal attached hook on top as a latch. Like a Masters lock. The note said,
Hey Mr. Scientist, confirm for me that the weight of this lock is very close to 5.28 pounds. You can only use things in the kitchen. Good Luck. O and just to tease you there is a small ruler for linear measurements for you
John rummaged through kitchen drawers and was shocked to find a spring balance, a linear analog weight scale with a hook at the end. It can’t be that easy he thought. Sure enough. The weight scale was from zero to 5 pounds! Now what?
He sat at the table and started working. He measured the lock first by the ruler. Was about 4x3x1.7 inches. But he could not measure the hook or latch part. He looked around the kitchen to see if there was any other standard measurement tool. NONE.
The usual cutlery, small and large pots and pans, cups, food, drinks like beer, soda cans, snacks. He weighed the lock on the weight scale just in case. Sure enough it went beyond the very last mark of 5 pounds. Looking at the lock he couldn’t tell what material it was made from. But certainly was some hard alloy. Not possible to cut.
Then he sat at the table drinking a beer bottle and thinking. All of a sudden he checked something on his laptop. Then he made ONE weight measurement (of something) on the spring balance. That came out to be 4.5 pounds. He followed that up with something else and jumped with joy. “I got it” he said. What exactly did John do?