Of course, r goes all around the z axis, but I'm just doing a slice through one of these vertical half planes, fixing the value of theta.

当然，r可以围绕z轴转圈，但我只做了一个垂直的半平面，对于一个确定的θ来说。

youdao

The Mini-Mill was just big enough for the job - half an inch less travel on the Y-axis would have made the job extremely difficult.

这台迷你机床的大小正好——要是在 Y 方向上再少半寸，那这活可就难干了。

youdao

Yes? Yeah, so I'm saying when you fix theta you get only a half plane, not a full plane I mean, it goes all the way up and down, but it doesn't go back to the other side of the z axis. Why?

请说，所以我说当固定θ时,得到的是半平面，而非全平面,它布满z-轴的一侧,但从不延伸到z-轴的另一侧，为什么？

youdao