Zoom in and make sure that the curve hits the guide line at the top, and the two points there are lined up with the guide exactly.

Step 4:
Complete the curve for the glass. You'll have to sort of wing it, using the photo as a guide. In the example here I pretty much ignored the details in the photograph and created a column inside the glass for the wires to attach to. Every make of lightbulb is slightly different so you can use some artistic license here. Make sure the end points line up on the guide exactly. Press CTRL-R to make the rulers visible (if they are not already visible). In the upper left corder of the ruler you will see too crossed dotted lines. This is the zero point of the ruler. By clicking and dragging on those lines, you can reposition where the zero, or origin point, of your drawing is. Now, drag the zero point on the rulers down to the bottom point of your glass curve so that the origin sits there exactly. This point will now be positioned at 0,0,0 when this curve is imported into Cinema 4D. Remove the guide line (important!) and the bulb image, and save the curve out as an Illustrator EPS file, version 6.0, no preview, no thumbnail.