## 8 Discussions and Conclusions
### Discussions on the Reviewed Studies  
A summary of the advantages and disadvantages in the application of methods and techniques, analysed and discussed in this section and Section 6.1, is provided in Table 2. This was made to provide a clear understanding of the more in-depth analysis of the research findings, which will be presented later on. Based on the values presented in this table, it is clear that, in order to meet the conservation needs of the artefacts, there could be some limitations. The accuracy and resolution of the obtained images are among the most common problems in this regard. Experimental methods and mathematical simulations are tools which might help to define restoration and conservation procedures [108; 147]. The combination of them is a powerful approach to analysing complex and unique works of art and prevent new or \begin{table}
\begin{tabular}{c c c c} \hline
**Techniques** & **Analysis Objectives** & **Advantages** & **Disadvantages** \\ \hline \multirow{6}{*}{Strain gauge} & Displacements and deformations & Suitable for multilayers objects & The strain is measured in the direction of the sensor. \\  & & Non-destructive technique & Needs of many sensors \\  & & & Sensor glued on the surface \\ \hline \multirow{6}{*}{Deformometric kit (DK)} & Dimensional changes & High accuracy & Data processing \\  & Capping deformation & In situ analysis (e.g., & Sensor glued on the surface \\  & & in a museum) & \\ \hline \multirow{2}{*}{Digital image correlation (DIC)} & Surface displacement & Non-destructive technique & Low quality if low contrast \\  & & Non-contact technique & of images \\ \hline \multirow{6}{*}{Photogrammetry} & Surface analysis & Low cost & Accuracy depends on the resolution \\  & & Measurement of three-dimensional deformations & of the camera and distance between \\  & & Measurement both on large and & \\ \cline{1-1}  & & small scale, e.g., timber members & \\ \cline{1-1}  & & Non-contact technique & \\ \hline \multirow{6}{*}{Laser scanner technique} & Surface out-of-plane displacement & High accuracy & Expensive \\ \cline{1-1}  & & geometry measurements & High resolution images are \\ \cline{1-1}  & & Non-contact technique & time-consuming \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of the main advantages and disadvantages of the analysed techniques. further degradations. This approach provides wide knowledge about the full response of wooden heritage to environmental cycles. Monitoring valuable artefacts and buildings requires the use of non-destructive techniques (NDT). However, results obtained by NDT can be affected by moisture content, compromising the validity of obtained data [148]. This aspect does not make the use of NDT useless, but it requires the consideration of the moisture content during the analyses in order to correlate it with the obtained results [149]. The degree of influence of MC on non-destructive tests also varies, accordingly, with the wood species [150]. The main limitation of experimental methods is the application of _point-strain_ measurements due to their need to bond the sensor to the work of art. The strong adhesive needed for high-quality measurements risks damaging vulnerable wooden surfaces. This drawback warranted the use of dummy samples, which mimic real artefacts. Alternatively, more conservative-friendly adhesives have been tested. Their use is still limited to short-term applications. For this reason, no-contact techniques, such as image-based ones, are sometimes preferred, but they are less accurate. Point-strain measurements, as recalled by their name, provide punctual information about the monitored surface. For anisotropic materials, such as wood, these collected data are non-representative of the whole object or building element; thus, an array of multiple sensors is employed. Deformation and strain measurement techniques, with climate parameter sensors, are used together to take an overall picture of the problem and avoid misleading results.