Two in-car instrument readings are almost always inaccurate, but that's not due to engineer error. This is the so-called "programmed lie" of the devices - some indicators deliberately overestimate or underestimate the readings for various reasons.
For example, the speedometer should show 5-10% higher speed than the actual speed so that the owner does not accidentally exceed it. The other device that shows inaccurate readings is the coolant temperature sensor. However, it is the opposite there.
The sensor reads 90 degrees when the system is working, although the actual operating temperature is around 110. This is done in order not to scare the user unnecessarily. But one thing is clear - these mistakes, as a rule, follow good intentions.
But there are also real problems with the electronics in the car. They appear when any of the main nodes, aggregates and sensors are damaged. In this case, it is necessary to carry out diagnostics in a car service. You should also be careful when buying the sensors in question, due to the abundance of low-quality and fake goods.