The Values: Dome Volume vs Dish Volume

There seems to be a contradiction in part 05:34 until 05:52 of this tutorial. Your explanation of dome and dish says that the dome is a negative value and that the dish is a positive value but when you simplify your explanation your conclusion states that the dome is a positive value and that the dish is a negative value. It isn't clear to me which values for the dome and the dish are negative or positive. Would some one be so kind as to clarify what the actual value of dome and dish is? In other words, which one really is the negative or positive value?

Shane,

I believe I understand your confusion. I think the following is stated clearly and looks correct.

"In this case, if we have a dished piston, we will add the volume of the dish to the clearance volume.

However, if the piston uses a dome, then this will protrude into the clearance volume effectively reducing the volume, so we would reduce this value from the clearance volume.

For simplicity, we'll represent a dished piston volume as negative, and a domed piston volume as a positive value."

Then the equation for clearance volume says to subtract the dome volume, and I think that's where you may have got confused.

If you're working with a domed piston, this likely is a bit more clear. Let's say the dome volume is +5cc. In that case you'd subtract 5cc.

If you're working with a dished piston, you don't have a dome volume, you have the opposite, you have a dish volume, which was prior stated will be represented as a negative value. When you subtract a negative value, ( - -x) this turns into addition. For example if you have a -15cc dished piston, when it comes time to subtract dome volume, you'd have - -15cc, which is + 15cc.

I hope that helps clear things, up. If not please let me know and I'll do my best to clear up any remaining confusion.