Count error rate of sam file

Question

[jianzheng934963534]

Hi I have aligned the fastq file to the reference genome and got a sam file. I know use "samtools stats" can get "error rate" of the sam file.

Is there any document shows how the error rate is calculated from the sam file? (since I want to seperately calculate the error rate of every read in the sam file instead of the average of the whole file)

Thanks!