Thank you for your inquiry regarding CMS871v3: Hospital Harm - Severe Hyperglycemia. Measure Observation 1, associated with the Denominator of the ratio, calculates the total number of eligible days of the inpatient hospitalization, which match the Initial Population/Denominator Criteria and did not meet the Denominator Exclusion Criteria. Measure Observation 1 calculates ‘eligible hospital days’ using the following parameters: *Eligible hospital days are not defined as midnight-to-midnight but are full 24-hour periods that start at the time of admission to the hospital (including emergency department and observation). *Eligible hospital days do not include the last day if it was less than a 24-hour period *Eligible hospital days are truncated to <=10 days. Therefore if the inpatient hospitalization exceeds 10 days, the measure will only use the first 10 days of the hospitalization to calculate measure observation 1. *Eligible hospital days range from day 2 to day 10 of the inpatient hospitalization. Day 1 is not considered an eligible hospital day because the measure does not count any hyperglycemic events that occur in the first 24 hours.   Based on the example you have provided, the value for Observation 1 would be 3, as you have calculated. You outline that observation 1 only counts the day if there was a blood glucose result on that day and that is incorrect. If the day meets all other parameters, it would be counted regardless of whether a blood glucose result is available on that day. We hope this helps.