SOLUTION

An instrument’s readings can change over time, even if the instrument itself isn’t faulty, due to the following reasons:

• Changes in temperature: Temperature variations can affect the physical properties of the instrument’s components, like resistance or dimensions, leading to altered readings.
• Aging of the instrument’s components: Over time, components can drift in value (e.g., resistors changing resistance, springs losing tension), affecting the instrument’s accuracy.
• Changes in the measured quantity: Even if the instrument is perfectly accurate, the readings will change if the quantity being measured changes. This is not a fault of the instrument, but rather a reflection of the changing conditions.