So the GBA clock frequency is 2^24 = 16.77216MHz, and the NDS bus clock frequency is 33.513982MHz. This is almost double, but if you calculate the error, it's off by 1207ppm:
16.777216 / (33.513982/2)
Assuming the NDS divides the clock by two...This would mean the GBA is 0.12% faster than the...