Precision Egg Timers

Why guess?

From the website:
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Egg Timers

This set of hand-blown timers has 3, 4, 5 and 6-minute vials covering every cooking condition from a small, room-temperature egg cooked at sea level to an extra-large, fresh-from-the-refrigerator egg cooked at 5000 feet above sea level (e.g., Denver) — where water boils at 203°F, not 212°F (95°C vs. 100°C).

Comes with simple instructions for turned stands or stands made from dimension stock.

Construction tips and compressible padding material for the ends of the vials are also included.
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$3.70 (stands not included).