The mass-abundance of the nine most abundant elements in the Earth's crust (see main article above) is approximately: oxygen 46%, silicon 28%, aluminum 8.2%, iron 5.6%, calcium 4.2%, sodium 2.5%, magnesium 2.4%, potassium, 2.0%, and titanium 0.61%.he mass-abundance of the nine most abundant elements in the Earth's crust (see main article above) is approximately: oxygen 46%, silicon 28%, aluminum 8.2%, iron 5.6%, calcium 4.2%, sodium 2.5%, magnesium 2.4%, potassium, 2.0%, and titanium 0.61%.
Choosing Disc Weight. Disc golf discs come in a variety of different weights. Most discs weigh between 165 and 175 grams. Some discs also come in special plastic blends designed to weigh less. The Professional Disc Golf Association regulates how heavy a disc can be based on the discs diameter.
The DVD-ROM drive in the photo is shown right side up; the disc would sit on top of it. The laser and optical system scans the underside of the disc. With reference to the photo, just to the right of image center is the disc spin motor, a gray cylinder, with its gray centering hub and black resilient drive ring on top. There is a disc-shaped round clamp, loosely held inside the cover and free to rotate; it's not in the photo.