Reliability is like an accurate scale, and you should get consistent results every time you weigh it. If the measurement results suddenly go up and down, just like "two Jin becomes one and a half Jin", then there is a problem with reliability and the scale is not accurate.
Validity, as expected, must be true and correct. If you want white sugar, the result is salt or rice, which is a question of effectiveness, that is, the measured content is not in line with expectations.