Black Friday: lifetime access is on a special offer in the app, until November 30. Black Friday: special offer on lifetime access, until November 30. Download
원자연대는 매우 정확한 시간 측정 방법입니다.wonjayeondae-neun maeu jeonghwaghan sigan cheugjeong bangbeob-imnida.The atomic time scale is a very accurate method of measuring time.