Monitoring and instrumentation are only of interest if they can explain the phenomena measured and any changes detected: ageing of the structure, consequences of works, deterioration of foundations, climatic impact, etc. External stresses are often the cause, wholly or partly, of changes in the parameters measured.
Temperature variations are one of the most obvious stresses, but we can also mention wind, traffic and many others.
These stresses will have an impact on the structure being studied, and may also have an impact on the instrumentation.
To answer the question that initially justified the installation of structural instrumentation, it is therefore essential to measure these external stresses as well.