An employer violates Lab. Code 512 and Wage Order No. 4 if it rounds actual clock in and out times for workers to the nearest 10th or 4th of an hour in calculating their meal and rest break periods–this is true even if (a question that the Supreme Court has not resolved) a similar policy of rounding hours for beginning and ending of the day’s work suffices for computing minimum wage and overtime pay. The meal break is short anyway. Rounding might deprive an employee of a third of the statutorily required work-free period. Also, a rebuttable presumption arises from an employer’s time records if they show that the employee did not receive the required 30 minutes of meal break and was not paid the one-hour substitute pay. That rebuttable presumption applies at all phases of the proceeding, not just class certification motions. The employer may rebut the presumption either with records showing that the employees voluntarily returned to work early or with representative testimony, surveys, and statistical analysis or other evidence.