Tafsir of Al-Mursalat 77:20

{To a determined extent} To a known measure of time that God has known and decreed: it is nine months, or less than that, or more than that.

{So We determined} So We measured that with a precise measurement.

{And excellent are We at determining} So excellent are We at determining it. Or: "So We were capable of that, and excellent are We at being capable of it." The first interpretation is more appropriate due to the reading of those who recited it as faqaddarnā (with a shadda), and due to His saying: {From a sperm-drop He created him and determined him} (Abasa: 19).

{Have We not made the earth a container? * Living and dead? * And We placed therein lofty, firm mountains and have given you to drink sweet water? * Woe, that Day, to the deniers.}