Hourglass

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Referring to a cylindrical or elongated structure with a central constriction likened, sometimes in only a very general sense, to an hourglass
References in periodicals archive ?
Measurement is continually reinforced in producing the sand timers and engaging in related activities.
Using an inclined plane, that is, a funnel, as a sand timer allows students to link the definition of simple machines to the idea that machines make work easier for people.
Students are told, "You have one minute to get ready for lunch," as I hold up the sand timer and invert it.