How is proportionality (Muwafaqah) between two numbers determined?

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Proportionality between two numbers is determined by an iterative process: subtract the smaller number from the larger number repeatedly. If the subtraction results in zero, the numbers are proportional (Mutanasiban). If a remainder is left, that remainder is subtracted from the smaller number, and this process of subtracting the later remainder from the preceding one continues until a number that perfectly divides the preceding number (other than one) is reached. The nature of the proportionality is defined by this final remainder: if the remainder is two, they are proportional by halves; if three, by thirds; if four, by fourths. Proportionality is also established if the smaller number, when repeatedly added to itself, equals the larger number. Furthermore, if the larger number is perfectly divisible by the smaller number, they are proportional. The proportionality is expressed as a single fraction relating the smaller to the larger, which occurs when the ratio is one-half or less.