## 1 Introduction  
An anomalous head position (AHP) is a postural deviation of the head from its physiological alignment with the body's axis [1]. It can manifest as lateral tilting, horizontal rotation, or alterations in chin elevation and depression, and it may present as combinations of these variations. AHP is a frequently observed clinical sign, with an estimated prevalence of approximately 3% in pediatric populations [2,3]. While not a diagnosis in itself, AHP often reflects compensatory mechanisms for ocular, orthopaedic, or neurological dysfunctions. These deviations can alter cervical spine mechanics and create muscle imbalances, which, over time, may lead to chronic pain, postural abnormalities, and other complications [3, 4, 5, 6, 7]. The causes of AHP can be broadly categorized into ocular and non-ocular causes [1, 8, 9, 10]. Non-ocular causes are often associated with musculoskeletal abnormalities, including congenital muscular torticollis and facial asymmetry [11, 12], the third most common congenital musculoskeletal condition in neonates [13, 14, 15, 16], while ocular causes typically involve the misalignment of the visual axes, prompting affected individuals to adopt compensatory head postures to optimize visual function. These include conditions such as strabismus [17, 18, 19] and nystagmus [20, 21, 22]; congenital syndromes like Duane syndrome [23, 24]; uncorrected refractive errors [25, 26]; and pathologies preventing foveal fixation, such as palpebral ptosis [27]. Patients with ocular AHP adopt compensatory head positions to enhance visual acuity, realize single binocular vision, or eliminate diplopia. For example, in cases of superior oblique muscle palsy, patients tend to tilt their heads towards the side opposite the affected eye to minimize vertical deviation and stabilize vision [28]. Understanding the etiology of AHP is essential for accurate diagnosis, as early intervention can prevent secondary complications like facial asymmetry and long-term musculoskeletal issues [29]. The quantitative measurement of AHP plays a key role in diagnosing its underlying causes and planning surgical or corrective treatments, particularly in pediatric patients where early intervention can significantly improve outcomes in terms of visual function and reduce the risk of long-term postural alterations [30, 31]. In early clinical practice, direct visual observation was a common method for evaluating AHP. However, this approach was found to produce significant measurement errors, with a tendency to overestimate the extent of AHP. Additionally, the accuracy of visual assessments diminished as the severity of AHP increased, with examiner estimates varying by as much as several dozen degrees in cases of more pronounced postural deviations [32]. Nowadays, various tools are used to measure AHP, ranging from traditional mechanical devices to advanced solutions based on electronic, magnetic, and ultrasound technologies, for which their reliability and validity have been studied over the past decades. Traditionally, mechanical goniometers have been widely used to assess head inclination, rotation, and elevation/depression. While these tools are valued for their affordability and simplicity, their accuracy can be influenced by the operator's experience, leading to variability in results [33]. The cervical range of motion (CROM) system represents a significant advancement in the measurement of head posture, combining both gravitational and magnetic inclinometers to allow for accurate measurements of head inclination, rotation, and elevation [34]. While highly reliable and validated for clinical use, the CROM device can be challenging to adapt for pediatric patients and may cause discomfort during prolonged use [35, 36, 37]. Innovative technologies originally designed for entertainment have recently been adapted for AHP measurement. The WiiMote system (Nintendo, Kyoto, Japan), for example, uses infrared sensors and a head-mounted transmitter to capture three-dimensional head posture data.