Welcome Xinzhi.
What did you try? Explain what is not working?
How speed works is explained here> How do we measure our speed with location.(speedometer) and did you read the posts in this post in comment #10 ?
Welcome Xinzhi.
What did you try? Explain what is not working?
How speed works is explained here> How do we measure our speed with location.(speedometer) and did you read the posts in this post in comment #10 ?