## 1 Introduction  
It is essential to determine the type, characteristics and scale of movements of a spatial structure or object under load from environmental forces to understand the potential probability of permanent damage or eventual destruction of the structure [1-6]. In metrology, various deformation monitoring and analysis approaches have traditionally been used [1,7-13] to ensure safe operation and usage of such structures. Furthermore, deformation may require very expensive restoration to be performed. The construction and management of such structures will be most cost-effective when the causes of deformation can be discovered and prevented. Currently, it remains an open question how best to detect significant deformations with an adequate level of precision [2,7,14-17]. In recent years, the progress of technology has resulted in improved precision of measurement systems, yielding more reliable results in deformation analysis of structures [18]. In addition to conventional terrestrial surveying methods using theodolites/total-stations, levels and similar surveying equipments, satellite-based positioning techniques (Global Navigation Satellite Systems, or GNSS, including GPS, GLONASS, Galileo, and Compass) have seen widespread use in structure monitoring. However, despite the many strengths and advantages of GNSS and conventional methods, there are still a few limitations due to the inherent geometric weaknesses of these systems, specifically, individual and atmospheric errors that affect their performance when used in high-precision work [1,14,17,19]. To overcome these techniques' disadvantages and increase their level of accuracy, it is necessary to use additional precise measurement equipment, such as inclination sensors, accelerometers, and terrestrial laser scanners [1,6,7,12,13,15,20,21]. Today, inclination sensors are often part of measurement systems that are used in static and kinematic applications of many disciplines, such as measuring the inclination of land or platforms to build upon, in aircraft flight systems, vehicle security systems, volcano monitoring, precise farming _etc._[22,23]. However, the studies are not many on the performance assessments of precise inclinometers and their use alongside other techniques for structural monitoring. In this study, a pair of inclination sensors of micro-radian precision were used alongside GPS for monitoring and determining the movements of a tall building and a geodetic monument (International GNSS Service-IGS continuous reference GPS station pillar), both located in Istanbul to the north of the North Anatolian Fault (NAF) [24-26]. Explaining merits and limitations of inclination sensors by comparing them to static and continuous GPS observations in deformation monitoring based on the drawn results of the case studies is purposed. The followed strategy and methodology for analyzing the deformations of case objects may constitute an example to the similar investigations. At a glance, large differences can be seen in the specifications of commercially-available inclination sensors [22]. The inclinometers used in the study are dual axes digital sensors, able to determine simultaneously the degree and direction of inclination, along with the temperature. With an opto-electronic sensor unit, 0.001 mm/m measuring accuracy is achieved [27]. Since these sensors do not employ mechanically-driven moving parts, they do not need any maintenance and provide long-term stability, which are useful properties for continuous deformation monitoring. In monitoring a tall reinforced concrete building which was damaged in the East Marmara Earthquake (M\({}_{\mathrm{w}}\) = 7.2) on 17 August 1999 [28], and then strengthened after the earthquake, two inclination sensors and dual-frequency geodetic GPS receivers were employed in the observation setup. Three static GPS campaigns were performed at six-month intervals.