Labour productivity is the ratio of output to man-hours. It measures the efficiency of a production process by calculating the amount of output produced per unit of labor input. The output can be measured in terms of goods or services, while the man-hours refer to the total amount of time worked by all the workers involved in the production process. In other words, labour productivity measures how much output is generated for each hour worked by the labor force. Therefore, the correct option is "output to man-hours".