A counter comprising: a first ring member having first indicia and a second ring member having second indicia, each of said first and second ring members being rotatable in increments about a common axis, one or both of said first and second indicia indicating a count； and a drive mechanism for rotating said first ring member and for rotating the second ring member after one or more predetermined degrees of rotation of the first ring member, wherein said drive mechanism comprises a pawl-and-teeth mechanism which comprises a first and second pawl engageable with a plurality of teeth, and wherein each of said first and second pawls comprise a driving engagement face for engaging in a driving engagement with one of said plurality of teeth, and a sliding engagement face for sliding over one of said plurality of teeth.一種計數器，其包含：一具有第一指標的第一環構件，及一具有第二指標的第二環構件，第一及第二環構件的每一者為可旋轉的而環繞一共同軸線增量，第一及第二指標的一或是兩者指示一計數；及用於旋轉該第一環構件及用於在該第一環構件旋轉一或更多預先決定的度數之後旋轉該第二環構件的一驅動機構，其中該驅動機構包括一棘爪-及-齒機構，該棘爪-及-齒機構包含一第一及第二棘爪可與複數個齒接合，及其中第一及第二棘爪的每一者包含一驅動接合面，用於與複數個齒之一接合呈一驅動接合；及一滑動接合面，用於滑動越過所述複數個齒的其中之一。
