THE PERIODS .
HOWEVER, THE MAIN QUESTION RAISED IN THIS CASE IN RESPECT OF THE INTERPRETATION OF COMMUNITY REGULATIONS CONCERNING SOCIAL SECURITY FOR MIGRANT WORKERS BEARS UPON THE WAY IN WHICH INSURANCE PERIODS MUST BE COUNTED TO DETERMINE THE PENSION OF A WORKER WHO HAS BEEN EMPLOYED IN DIFFERENT COUNTRIES WHEN THE UNITS USED IN THOSE COUNTRIES FOR SUCH CALCULATIONS ARE DIFFERENT . THE NECESSITY TO MAKE USE OF HOMOGENEOUS UNITS FOR SUCH COMPUTATION PURPOSES MUST BE RECONCILED WITH THE REQUIREMENT THAT THE REFERENCE UNIT ADOPTED BY ANY MEMBER STATE TO ASSESS INSURANCE PERIODS IN THAT STATE SHOULD BE RESPECTED . THIS REQUIREMENT MEANS IN PARTICULAR THAT, FOR THE PURPOSES OF ESTABLISHING THE RIGHT TO A PENSION IN ONE MEMBER STATE AND OF DETERMINING THE AMOUNT THEREOF, IT IS NOT POSSIBLE TO TAKE INTO ACCOUNT INSURANCE PERIODS COMPLETED IN THAT STATE, WHICH, EVEN AFTER AGGREGATION WITH PERIODS COMPLETED IN OTHER MEMBER STATES WITHIN EACH RELEVANT UNIT OF TIME, ARE SHORTER THAN THE PERIOD ADOPTED BY THE LEGISLATION OF THE FIRST STATE .
BUT THIS REQUIREMENT CANNOT RULE OUT THE POSSIBILITY OF CONVERTING THIS PERIOD INTO ANOTHER UNIT OF TIME, FOR THE PURPOSES OF COMPENSATORY CALCULATIONS NECESSARY TO AVOID DUPLICATION OF ONE AND THE SAME PERIOD, WHICH IS THEORETICAL IN RESPECT OF ONE MEMBER STATE BUT HAS ACTUALLY BEEN COMPLETED IN ANOTHER MEMBER STATE, SUCH PERIOD BEING, HOWEVER, COUNTED IN DIFFERENT UNITS OF TIME .
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THEREFORE, THE FRACTION USED IN SUCH A CASE FOR PRO RATA CALCULATIONS SHOULD HAVE ITS DENOMINATOR AND NUMERATOR DETERMINED ACCORDING TO THE SAME UNIT OF TIME FOR ALL THE COUNTRIES CONCERNED, AND THIS UNIT OF TIME MUST BE THAT OF THE STATE HAVING THE SHORTEST INSURANCE PERIOD, WHEN THIS PERIOD IS A FRACTION OF THE OTHER PERIOD . OTHERWISE, THIS UNIT MUST BE A MULTIPLE COMMON TO THE VARIOUS UNITS OF TIME IN QUESTION .
Decision on costs
THE COSTS INCURRED BY THE COMMISSION OF THE EEC WHICH HAS SUBMITTED OBSERVATIONS TO THE COURT ARE NOT RECOVERABLE AND AS THESE PROCEEDINGS ARE, IN SO FAR AS THE PARTIES TO THE MAIN ACTION ARE CONCERNED, A STEP IN THE ACTION PENDING BEFORE THE BELGIAN CONSEIL D' ETAT, THE DECISION AS TO COSTS IS A MATTER FOR THAT COURT .
Operative part
THE COURT
IN ANSWER TO THE QUESTION REFERRED TO IT BY THE BELGIAN CONSEIL D' ETAT ( SECTION D' ADMINISTRATION, VITH CHAMBER ) BY ORDER OF THAT COURT OF 11 MAY 1967, HEREBY RULES :
1 . WHEN PERIODS ASSIMILATED TO INSURANCE PERIODS UNDER THE LEGISLATION OF ONE MEMBER STATE OVERLAP INSURANCE PERIODS ACTUALLY COMPLETED IN ANOTHER STATE AND GIVING A RIGHT IN THAT STATE TO A PENSION, AND WHEN THE UNITS OF TIME ADOPTED BY THE LEGISLATION OF THESE STATES ARE DIFFERENT, IT IS NECESSARY, AS REGARDS BOTH THE DENOMINATOR AND THE NUMERATOR OF THE FRACTION FOR PRO RATA CALCULATIONS, TO CONVERT THESE UNITS INTO THE SMALLEST OF THE UNITS OF TIME ADOPTED BY THE STATES CONCERNED WHEN THIS SMALLEST UNIT IS A FRACTION