In robotics, making a precisely straight robot or a precise 90/180 degree turn right/left can be challenging, especially if you are using trial-and-error to figure out how long to turn the robot. There are some methods to do improve accuracy:

	Trial and Error, without sensors	Gyroscope Sensor	Odometry/Wheel Encoder Sensor
Simplicity	Easy, just play with delay values	Medium-Hard, may require knowledge of  i2c/spi protocols and/or reading the sensor datasheet, expensive ~$20-40	Medium, may require basic geometry in measuring angles, coding is straightforward. ~$5-20
Accuracy	Unaccurate, speed changes  when voltage drops	Accurate, relies on the inertia of a spinning disk called a gyro to measure the angular velocity. During drift, it finds the angular displacement and auto-corrects to  the original angle.	Accurate on 90 degree/180 degree turns with right wheel diameter/chassis diameter calculations, but can't be used in moving forward because of drift.
Pros	Easy-to-code	Accurate on both straight and degree turn robots	Moderately inexpensive, accurate degree turn  with correct geometry, straightforward coding.
Cons	Requires a lot of adjustment when the  voltage  drops to match speed	Requires some intermediate coding skills, and is costly.	Doesn't sense drift!

Each has its own advantages, but I will use the gyroscope method in my future robot posts, because it is accurate in both going forward as well as 90 degree turns. Unlike odometry, which only senses the turns the motor traveled for each wheel, I could compensate for the angular drift when moving straight, because the gyro knows the difference between now's angle and the angle we started with.