CJL-101 - The original 203 was supposed to be 40 degrees. occassonally, from a lot of use, the foam material that the base was made of would compress which might change the angle as much as 5 degrees. The 204 does not use a foam to correct this.
We also learned that stones that are undersized beyond tolerance (.010) would also change the angle. On the 204, we tightened up the tolerance.
The 204 is a better tool simply by virtue of an additional 20 years of experience with the 201, 202 & 203 models.
Hope that helps.
sal