The Wiimote and the Nunchuck use the same 3d accelerator part. They get a *rate of change* of velocity in x, y, z.

Since gravity is a known component, you can use this to estimate current roll and current pitch but not current yaw. The estimates are not very accurate if there are other strong acceleration components like shaking.

The Wiimote has a camera that can analyze the picture to find the "sensor bar" lights. It can then estimate current yaw, and fine-tune the current roll and pitch estimates. The Nunchuck does not have any way of detecting the sensor bar, of course.

With acceleration and a known starting condition, you can also estimate velocity, and with velocity, you can also estimate absolute position. These sensors are pretty noisy, so don't expect much in the way of position tracking.

The Wii Motion Plus adds a three axis gyro sensor to the above capabilities. It's not able to determine current yaw, pitch or roll. It's only able to determine *rate of change* in yaw, pitch and roll.

Just as with orthogonal velocity, you can also estimate the absolute rotational position (current yaw, current pitch, current roll) given the rotational velocity and a known starting condition.