About Goniometer
Editorial & methodology · Updated July 2026
goniometer.io publishes clinical reference guides on measuring joint range of motion, and is the home of Goniometer: Range of Motion — an iPhone app that turns the phone into a validated digital goniometer. Both are made by one clinician, and this page explains who that is and the standards every guide is held to.
The clinician behind Goniometer
Kevin Lan, OTR/L, ATP is a licensed occupational therapist and assistive technology professional with more than eight years of clinical experience across acute care, inpatient rehabilitation, home health, and outpatient neurorehabilitation. His practice focus is spinal cord injury and neurological populations, including work in a wheelchair seating and positioning clinic — settings where measuring and documenting joint range of motion is part of the daily workflow.
Goniometer exists because the tool he wanted at the bedside didn't: a goniometer that guides placement, shows the normal range next to every reading, and turns measurements into documentation without a laptop. The app is designed around those clinical workflows, and every guide on this site comes from the same perspective — how measurement is actually done and charted in practice.
How the content is written and reviewed
- Normative values come from one source. Every normal range of motion value on this site and in the app uses American Academy of Orthopaedic Surgeons (AAOS) reference values, kept deliberately consistent so the site, the app, and the printable chart always agree.
- Technique follows standard texts. Goniometer placement — fulcrum, stationary arm, moving arm — follows Norkin & White's Measurement of Joint Motion, the standard goniometry reference in OT and PT education.
- Claims cite peer-reviewed research. Accuracy and reliability statements link to the underlying studies (for smartphone goniometry, the canonical citation is Keogh et al.'s 2019 systematic review in PLOS ONE). References are listed on each page in order of appearance; see the accuracy evidence.
- Every clinical guide is reviewed by Kevin Lan, OTR/L, ATP before publication, and the "Updated" date on a page changes only when its content substantively changes.
- Corrections are welcome. If you find an error, write to support@goniometer.io and it will be checked against the references and fixed.
About the app
Goniometer: Range of Motion measures 47 movements from the cervical spine to individual finger joints using the iPhone's gravity-referenced motion sensors, with animated placement guidance and AAOS normal values on every screen. Measuring is free without limits; patient data stays encrypted on the device and is never collected. It is built and maintained by the same clinician who writes this site.
Questions or feedback? Reach the developer directly at support@goniometer.io, or see the support page.
Related pages
Goniometer is an educational and reference tool. It is not a medical device and is not intended for diagnosis or treatment decisions.