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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.

Please enter your results in the table below. You may enter as many results as you like THOUGH PLEASE REFRESH THIS PAGE BEFORE EACH NEW ENTRY. Each time you Submit, you will send us the information written in the cells below.

 Weather conditions (sunny, cloudy, etc): Indoors: range in measured position (in metres): Indoors: number of walls between you and sky: Outdoors range in measured position (in metres): Outdoors: details (how far from trees/buildings): The device you used (optional): Your first name*: Age range: Select here Primary Secondary (Years 7-9) GCSE A-Level Other The first half of your post code*: * These are optional – the name is so we could mention you in the end of week report and the postcode is to see where people are taking part. We won’t use this information for anything else. Verification: