What Is Mag-Cal For Bone Support?
Calcium and magnesium (Cal-Mag) supplements abound, most of which come in a 2:1 ratio of Calcium to magnesium, which healthcare practitioners consider optimal for bone health. However, Cal-Mag also comes in a 1:1 ratio of calcium to magnesium and, less frequently, in so-called "reverse-ratio Cal-Mag," which supplies twice as much magnesium as calcium.

https://www.nationalnutrition.ca/bone-health/cal-mag/mag-cal-reverse-ratio.html