For measuring the range of motion of a joint with precise angular measurements but without identifying the axis of rotation.
 
Research Articles:
Amirreza, S., Shahab, I., Hasan, D. & Mansour, S. (2014). A Comparison of Glenohumeral Internal and External Range of Motion and Rotation Strength in Healthy and Individuals with Recurrent Anterior Instability. The Archives of Bone & Joint Surgery, Vol 2, Iss 3, P215-219 (2014), (3), 215.

Ferguson, S. L., Eonho, K., Dong-H., S. & Bemben, M. G. (2013). Comparing the Effects of 3 Weeks of Upper-Body Vibration Training, Vibration and Stretching, And Stretching Alone On Shoulder Flexibility in College-Aged Men. Journal of Strength & Conditioning Research (Lippincott Williams & Wilkins), 27(12), 3329-3334.

White, S. B., Bemben, D. A., Knehans, A. W. & Bemben, M. G. (2005). Effect of Continuous Passive Motion (Machine-Assisted) Exercise As an Alternative Form of Training on Physiological Profiles of Women Aged 40-65 Years. Journal of Strength & Conditioning Research (Allen Press Publishing Services Inc.), 19(3), 634-639.

This device measures the range of motion of a joint with precise angular measurements.
 
Research Articles:
Farooq, M. N., Mohseni Bandpei, M. A., Ali, M. & Khan, G. A. (2016). Reliability of the universal goniometer for assessing active cervical range of motion in asymptomatic healthy persons. Pakistan Journal of Medical Sciences, 32(2), 457-461. doi:10.12669/pjms.322.8747

Hirschhorn, A. D., Lockhart, J. W. & Breckenridge, J. D. (2015). Can a physical activity monitor provide a valid measure of arm elevation angle? A study to assess agreement between the SenseWear Mini Armband and the universal goniometer. BMC Musculoskeletal Disorders, 16(1), 1-9. doi:10.1186/s12891-015-0507-4

Otter, S. J., Agalliu, B., Baer, N., Hales, G., Harvey, K., James, K., & Wong, D. (2015). The reliability of a smartphone goniometer application compared with a traditional goniometer for measuring first metatarsophalangeal joint dorsiflexion. Journal of Foot & Ankle Research, 8(1), 1-7. doi:10.1186/s13047-015-0088-3

For measuring the flexibility of hamstrings and lower back.
 
Research Articles:
Adegoke, B. A., Akpan, G. A. & Mbada, C. E. (2012). Normative Values Of Lower Back And Hamstring Flexibility For Nigerians Using The Modified Sit-And-Reach Test. Journal Of Musculoskeletal Research, 15(3), -1.

Kawano, M. M., Ambar, G. Oliveira, B. R., Boer, M. C., Cardoso, A. G., & Cardoso, J. R. (2010). Influence of the gastrocnemius muscle on the sit-and-reach test assessed by angular kinematic analysis. Brazilian Journal of Physical Therapy / Revista Brasileira De Fisioterapia, 14(1), 10-15.

Piva da Cunha Furtado, O. L. Pereira Morato, M., Potenza, M., & Gutierrez, G. L. (2016). Health-Related Physical Fitness among Young Goalball Players with Visual Impairments. Journal of Visual Impairment & Blindness, 110(4), 257-267.