Validity and reliability of smartphone magnetometer-based goniometer evaluation of shoulder abduction – A pilot study

•Built-in magnetometer in smartphone is examined for use in joint angle measurement.•Magnetometer-based goniometer demonstrates validity against a standard goniometer.•Smartphone magnetometer-based goniometer can measure shoulder abduction reliably.•Inter-rater and intra-rater reliability is comparable against the standard universal goniometer.•Relative ease-of-use and portability of a smartphone goniometer is promising.