The policy outlined in my most recent syllabus is summarized as follows:
Attendance in class and laboratory is required. Students will lose 2.5% credit for each unexcused absence from class or laboratory, up to the loss of one and one-half letter grades. Students will be granted one waiver for a missed class and no waivers for missed laboratories. With regard to in-class queries, each student is allowed to “pass” twice. After these “passes” have been used, the student will lose one point off the final grade for failing to provide an answer; answers that suggest a serious lack of preparation may also lose one point off the final grade.