The pitch circle diameter (PCD) of a gear is a vital measurement when using gears. When you mesh two gears together, the teeth need to mesh to a precise distance, if too deep then the teeth will bind and wear, too shallow and you will get excessive back lash and risk damage to the teeth.
Burping gas that smell strongly of rotten eggs is actually indicative of the presence of sulfur in our stomach. This is the reason why this type of burps is commonly known as sulfur burps. The smell of sulfur burps or rotten egg burps usually comes from the presence of hydrogen sulfide.
No matter where it's coming from, the rotten-egg smell usually associated with sulfur is an unpleasant one, and it usually means something is wrong. The smell may actually be caused by a sulfur compound, such as hydrogen sulfide -- which originates in fetid swamps and sewer pipes -- or sulfur dioxide -- a byproduct of fossil fuel combustion.