"The sun and the moon should be taken into account in the calculation" (Al-Rahman: 5).
One of the most important reasons for the advancement of nations and their civilization is the science of arithmetic. The calculation of the calendar is not a minor matter but an essential and vital matter. If the components in the arithmetic equation are different the result will be different too. If the calendar calculation is based on the moon calculation only or the calculation is based on the sun calculation only the result will be different from the calculation based on both the sun and the moon.
The letter and in the verse means that both the sun and the moon must be taken into account in the calculation. And if the verse contained "or" the calculation would have been either the lunar calendar or the solar calendar. The lunar solar calendar calculates the position of the earth in orbit around the sun taking into account the calculation of the moon's rotation around the earth. The program also calculates the times of day based on the degree of inclination of the sun on earth and shows the possible sun and moon directions taking into account the direction of the head. And the position of the moon around the earth works like a pendulum to calculate the position of the earth around the sun which is also very precisely "4 minutes". According to this calendar the month of Ramadan falls in autumn when all people around the world have the same number of hours of fast. And the answer to the question How do some people sometimes fast into the night "according to the lunar calendar" in summer when the sun does not set in these countries in summer?
The main problem is that this calendar opens the door to a lot of questions! Was the legacy hiding some facts? This kind of calculation is the practical application of the verse. Clinging to religion is an individual responsibility: "and stopping them because you will be held accountable." (Al-Saffat: 24). Nobody will be able to answer a single question for you.