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Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
There used to be a metric calendar, as well as metric clocks. The metric calendar, or "French Republican Calendar" divided the year into 12 months, but each month was divided into three 10-day weeks. Each day had 10 decimal hours. Each hour had 100 decimal minutes. Due to lack of popularity, the metric clocks and calendars were ended in 1795, three years after they had been first marketed.
In 1864, the first barbiturate (barbituric acid) was synthesized.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.

