Enter the average time in days between discoveries of new software defects during the first month after delivery (the end of QSM Phase 3). To calculate the MTTD, take the reciprocal of the defects found during this month and multiply by 4.333 (weeks per month), and the days per week for the operational environment. For example, if there were 5 errors during the first month of operation and the system runs 7 days per week, the average MTTD value would be (1/5) * 4.333 * 7 = 6.07 days between defects. If there are no defects in the first month, the MTTD in the first month cannot be calculated. In this case, you should leave this field blank, or you may want to enter the maximum number of days the system runs in that month. The actual MTTD value entered for the project is used to calculate 5-star ratings for reliability.