These are results of tests carried out in October and December 2014. Tested were the following GPS telemetry, GPS data loggers and a hand held GPS.
GPSFlight STX900e telemetry, embedded GPS unit ublox LEA - S5
BRB 900 MHz GPS Telemetry, Lassen IQ series GPS receiver
TLA 900 MHz GPS Telemetry, ublox 6 series GPS receiver
Holux 1200e GPS data logger
Tripmate 852 GPS data logger, GPS chipset, MTK
Garmin etrex H
The benchmarks were 2 state survey marks (SSM) 35 km apart in Sydney, Australia. The data sheets for these marks were provided by NSW Spatial Exchange. Devices were left on the marks for 15 minutes at mark 1 and 30 minutes at mark 2.
All devices are DGPS capable.
All use WGS 84 height datum
Mark 1 (60% sky view approx)
Mark 2 (80% sky view approx)
Deviation from position, altitude
1= 9.5 ft, 18.4 ft (7 sats)
2= 3.5 ft, 4.6 ft (10 sats)
BRB 1= 11.9 ft, 16.2 ft (7 sats)
2= 13.6 ft, 3.7 ft (10 sats)
TLA 1= 12.6 ft, 14.8 ft (7 sats)
2= 14.2 ft, 3.6 ft (10 sats)
Holux 1= 29.3 ft, 40.3 ft (7 sats)
2= 9.8 ft, 20.4 ft (10 sats)
Tripmate 1= 18.5 ft, 27.3 ft (7 sats)
2= 7.1 ft, 1.6 ft (10 sats)
Garmin 1= 45.6 ft, 10.8 ft (6 sats)
2= 13.5, ft, 23.0 ft (10 sats)
Looking at the data from these readings, all these GPS unit's positional data "drift" around the static mark but on average give very acceptable accuracy for my purpose IMO. I would think that these devices would need to be left for 1 hour to stabilise properly.
I use these GPS devices on World kite altitude record flights and in the remote zone I use and at altitudes up to 16,000 ft, there are 12 or even 13 satellites acquired. That's way more than most people seem to get in urban or forested areas. Any of these units will give me better than 0.08% accuracy over my height profile. If you want better accuracy then you need something like a Trimble Total Station or a similar survey grade GPS with additional augmentation. It depends on how much you pay and your understanding of the usage and limitations. People sometimes have unrealistic expectations of what is wonderful technology at a dirt cheap price. I originally paid $600 for the GPSFlight telemetry 9 years ago. The BRB was $300, TLA around $250, Garmin etrex $99, Holux $100, Tripmate $50. I can remember handheld readily available GPS units were close to $800 about 20 years ago. They are getting cheaper and cheaper but I cannot vouch for the quality or accuracy of all cheap units. Manufacturers of consumer grade GPS units usually make claims of sub 3 meter for position and sub 5 meters for altitude under good conditions. It seems it's still tremendous bang for buck seeing these devices can place you within a 10 meter square on the surface of the earth with 40 billion square metres.