раз в шесть месяцев
• The governor should be tested at least every six months.
• Under normal operating conditions, the instrument should be lubricated at six-monthly intervals.
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Русско-английский научно-технический словарь
на Gufo.me
• The governor should be tested at least every six months.
• Under normal operating conditions, the instrument should be lubricated at six-monthly intervals.