Historically, statistics of “hours of work” were always linked with statistics of wages. Statistics of wages and hours of work was one of the topics on the agenda of the First International Conference of Labour Statisticians in 1923, which adopted a resolution covering the type of statistics which were relevant (normal hours of work and actual hours of work). No definitions were provided at the time.
The Convention (no.63) concerning statistics of wages and hours of work, adopted by the International Labour Conference in 1938, set minimum standards for statistics of average earning and hours actually worked in the principal mining and manufacturing industries, including building and construction and statistics of time rates of wages and normal hours of work in the same industries, as well as statistics of wages and hours of work in agriculture. This Convention provided a definition of normal hours of work, very much in the same lines as the current definition, but no definition of hours actually worked.
It was not until 1962, however, that the Tenth International Conference of Labour Statisticians adopted an international definition of hours actually worked. The Tenth International Conference of Labour Statisticians also discussed a definition of hours paid for. It was not adopted, however, given wide differences in payment of holidays and other periods of inactivity.
Hours actually worked
Much before the hours actually worked had been defined for statistical purposes, ILO Conventions had defined it for legal and regulatory purposes. These Conventions defined hours actually worked as the hours, during a specified reference period, when (paid) workers are at the disposal of an employer, that is, when they are available to receive orders from an employer or a person with authority.
For example, the Hours of Work (Commerce and Offices) Convention in 1930 first ascribed "time worked" to availability periods, explicitly excluding "time for rest", when workers are not available to work:
The term "hours of work" means the time during which the persons employed are at the disposal of the employer; it does not include rest periods during which the persons employed are not at the disposal of the employer .
"Rest periods" are periods when workers are not available to work. However, short breaks are difficult to identify separately from periods of “availability” because they are short and easily interchangeable. For example, workers may prefer to take a coffee break (an unscheduled resting period) during stand-by periods (an availability period).
That may be the reason why the Hours of Work and Rest Periods (Road Transport) Convention adopted in 1939 included “periods for rest below a certain length” (when workers are neither working nor available to work):
The term "hours of work" means the time during which the persons concerned are at the disposal of the employer or of any other person entitled to claim their services, or in the case of owners of vehicles and members of their families, the time during which they are engaged in their own account in work connected with a road transport vehicle, its passengers or its load, and includes -
(i) time spent in work done during the running time of the vehicle;
(ii) time spent in subsidiary work;
(iii) periods of mere attendance; and
(iv) breaks for rest and interruptions of work, which breaks or interruptions do not exceed a duration to be prescribed by the competent authority .
The current international definition of hours actually worked is drafted on similar lines.
Normal hours of work
“Normal hours” was first defined in international standards by the Convention concerning Statistics of Wages and Hours of Work (1938) as follows:
The statistics of normal hours of work shall show the hours -
(a) fixed by or in pursuance of laws or regulations, collective agreements or arbitral awards;
(b) ascertained from organisations of employers and workers, from joint bodies, or from other appropriate surveys of information, in cases where hours are not fixed by or in pursuance of laws or regulations, collective agreements or arbitral awards.
“Normal hours of work”, where not fixed by or in pursuance of laws or regulations, collective agreements or arbitral awards, shall be taken as meaning the number of hours per day, week or other period, in excess of which any time worked is remunerated at overtime rates or forms an exception to the rules or custom of the establishment relating to the classes of wage earners concerned.
Similar definitions were later adopted by the Recommendation dealing with the reduction of working time . The current international definition is drafted on similar lines.