## 2 Test Procedure  
Two GPSMap 66 units (labeled blue and green) were used to confirm reproducibility of results during testing. The test procedures and analysis methodologies used for the equipment evaluation are common to evaluate GNSS equipment performance, well documented in the literature and require no further description.  
Testing conditions ranged from ideal horizon-to-horizon open sky to indoors with signal attenuation of over 25 dB. The following tests are described herein:  
1. Single point static positioning in a high specular multipath environment occurring on a building roof top. In this case, a high grade geodetic GNSS external antenna was also tested with the units under evaluation to demonstrate antenna characteristic importance in such an environment.
2. Single point and differential static GNSS in a relatively low multipath environment occurring in open areas.
3. Vehicular testing on relatively open roads with units mounted on the vehicle roof to allow access to satellite lines-of-sight.
4. Indoor signal analysis with signal attenuation of over 25 dB.
5. Extreme urban canyon signal analysis testing.  
A point precisely (within 1-2 cm) known in ITRF 2014 (basically equivalent to WGS84, given the accuracy required for the present assessment) was used for some of the single point static tests and served as base to establish coordinates of other points in precise differential GNSS mode when needed. For differential static and vehicular tests, a high-end R10 geodetic receiver (Trimble, Sunnyvale, CA, USA) was used to derive reference positions with accuracy of 10 cm or better. Hourly NASE broadcast ephemerides were used to generate the GPSMap 66 and P10 results.  
Figure 1: Garmin GPSMap 66 and Huawei P10 units tested.  
Measurements were processed using RTKLib in forward mode for both single point and differential positioning. No filtering was used when processing data in single point mode in order to assess raw code data performance, with the understanding that this would not be done in practice. Some GPS measurements were also reprocessed in PPP mode using the Natural Resources Canada (NRCan) latest CSRS-PPP online software calculator (V 1.05 11216) which provides geodetic coordinates in ITRF 2014; the software processes L1/L2 or L1 only, both with carrier phase measurements.  
In order to show the code quality of the units used, differences between code and carrier phase measurements in a low multipath environment are depicted in Figure 2 using the code-minus-carrier approach over periods of 500 s. As expected, the R10 code quality is best, with RMS value of 0.19 m, while corresponding values are 1.15 m and 2.26 m for the GPSMap 66 and P10, respectively. Continuous carrier phase sequences longer than 500 s were rare with the P10 but normal with the GPSMap 66 under clear sky conditions, likely due to Android 8 operating system limitations. The P10 code performance is similar to that of the Huawei Mate 9 tested by [3] and other Android phones (e.g., [4]). The GPSMap 66 performance obtained with Galileo E1 satellites was similar to the above obtained with GPS and no ambiguous E1 code measurement issue arose, unlike the case of some Android phones (ibid). A comparison of instantaneous Doppler and pseudorange differences is shown in Figure 3 for the GPSMap 66 and P10 units, respectively. The P10 data was collected in a moving vehicle.  
Figure 2: Quality of GPS L1 code measurements of Trimble R10 (**top**), Garmin GPSMap 66 (**middle**) and Huawei P10 (**bottom**) in a low multipath environment using the code-minus-carrier method.