Discussion note for gyro precsion (#317)

* Discussion note for gyro precsion

* Wrong sig

docs/reference/motors/motor/angle.md

@@ -6,11 +6,11 @@ Get the current angle of the motor's rotation in degrees.
 motors.largeA.angle()
 ```
 
-When a motor is started for the first time, or after a reset, it's angle of rotation starts at `0` degrees. A complete rotation (a turn in a full circle) is `360` degrees. At `360` degrees, the motor angle gets set back to `0`. So, one and a half turns adds up to `540` degrees of total rotation but the motor only cares about the current angle from `0` degrees which is `180` degrees.
+When a motor is started for the first time, or after a reset, it's angle of rotation starts at `0` degrees. A complete rotation (a turn in a full circle) is `360` degrees. At `360` degrees, the motor angle doesn't go back to `0` but keeps counting in degrees. So, one and a half turns adds up to `540` degrees of total rotation.
 
 ## Returns
 
-* a [number](/types/number) which is the current angle of rotation for the motor. The value returned is the number of degrees from `0` to `359`.
+* a [number](/types/number) which is the current angle of rotation for the motor.
 
 ## Example
 

libs/gyro-sensor/docs/reference/sensors/gyro/angle.md

@@ -3,11 +3,35 @@
 Get the current rotation angle of the gyro.
 
 ```sig
-sensors.gyro2.rate()
+sensors.gyro2.angle()
 ```
 
 When the brick changes its position, it's moved in the direction of one of the axes used to measure three-dimensional space. Depending on where the gyro sensor is attached, it can measure the difference in angle from where it was before it moved. This angle is measured in degrees. The angle is the number of degrees rotated from where the gyro was last [reset](/reference/sensors/gyro/reset).
 
+## ~hint
+
+## Accuracy and calibration
+
+Gyro sensors aren't perfectly accurate. Sometimes, because of temperature and changes in the way elecricity behaves in the sensor, the gyro returns a small error in it's measurement. This causes the gyro sensor to return an incorrect value for the amount of angle it detected. This might make your robot drive off course and not go to where you want it to.
+
+### Drift
+
+If you want to turn the tank or robot you built to the left by 45 degrees, you might run the motor on the right side until the gyro reported that you turned by 45 degrees. What if the gyro was getting an error of 4 degrees every time it measured an angle? You may have actually turned 49 degrees when you expected to turn 45 degrees. Well, that might not be too bad if you use the gyro's angle value only once. It's fine if you just wanted to turn and stop or drive a short distance in only that direction.
+
+The problem is that when you need to read the angle measurement frequently, the amount of error in the angle measurement may continue to increase. If the sensor thought it moved by 45 degrees the first time instead of really 49 degrees, your second turn will put you at 98 degrees when the sensor said 90 degrees. If you want a robot to turn right 90 degrees and drive for 5 meters, it might actually turn 98 degrees and drive 0.7 meters off course before it stops. This error in the sensor's measurement is called _drift_.
+
+### Time to reset
+
+If errors in the angle values returned by the gyro sensor are making your project not work right, then it's time to **[reset](/reference/sensors/gyro/reset)**. A reset will return the gyro sensor's current angle value back to `0` and _calibrate_ for drift. Calibration is the process of finding out how much error there is in a sensor's measurement and then removing the error from the value returned to your program.
+
+Are you using a gyro sensor in your project and need accuracy for your angle values? You should reset the gyro sensor at a regular intervals to improve precision in the values reported to your program.
+
+### Handling imprecision
+
+Unfortunately, the angle values returned from the [gyro sensor](https://education.lego.com/en-us/products/ev3-gyro-sensor-/45505) are going to have some inaccuracy even when calibrated. The error could be as muchs as 3 degrees in either direction of rotation (`3` or `-3` degrees). So, you need to decide how precise your angle measurments need to be and have your code handle the possiblity that angle values aren't always exact.
+
+## ~
+
 ## Returns
 
 * a [number](/types/number) that is the current angle of rotation in degrees.