Omer

While Emel returned home, Omer ate corn.

...that Omer which was every mans daily portion of Manna, is computed to have bin more then might have well suffic'd the heartiest feeder thrice as many meals.

And it came to pass, that on the sixth day they gathered twice as much bread, two omers for one man: and all the rulers of the congregation came and told Moses.

The counting of the Omer—the Sefiras HaOmer—is a mitzvah.