Close
Close
Measurement at home

# Where on Earth am I?

## How good is theGlobal Positioning System (GPS)?

• Is GPS better indoors or outdoors?
• How accurate is GPS?
• What is the difference between accuracy, resolution and precision?

Estimated time: 30 minutes.
No prior knowledge needed.

### Equipment required

• Smartphone or tablet with GPS app reporting decimal longitude and latitude to 6 decimal places.
• Paper and pencil for results.

### Risks

• Ensure you have permission of the device’s owner before using it in this experiment.
• Remove dirty footwear before entering house.
• Don’t report your latitude, we want the range of results in metres.

## Steps

Watch the video

1. Find an app that reports longitude and latitude in decimal format to six decimal places (e.g. 51.000001, -0.816161). Ensure it works on your device at desired location/s (some tablets need to be in range of wi-fi). Good apps are GPS Status and Physics Toolbox GPS.
2. We need results from two positions: inside and outside a building respectively. In each case, follow steps 3-7.
3. At your measurement position, start app and wait 2 minutes for values to settle. Write down latitude reading. If readings still change, take a photo and jot down the value from that.
5. Repeat step 4 enough times to collect 5 latitude readings.
6. Calculate the range between the smallest and largest values. e.g. 51.000051 - 51.000001 = 0.000050.
7. Convert decimal latitude range to metres by multiplying by 110.
8. Perform steps 3 to 7 indoors and also outdoors (away from trees and buildings).

## Thoughts, tips and information

### SI measurement units

• metre (m) for position
• second (s) for time

### Challenge Topics

Measurement Science, Maths, Geography.

• How long do readings take to settle? What is happening during this time?
• Some GPS devices use an additional signal from a nearby receiver of known fixed location to dramatically improve accuracy.
• Clocks on board satellites have enough resolution to show effects to relativity.