understanding regions.bed file
Hello brentp,

I am wondering about the output of the region.bed file created by a sample(NA12156 - BAM Test files) which i downloaded from [here](https://www.ncbi.nlm.nih.gov/tools/gbench/tutorial6/)

regions.bed output-file:

`head sample-output.regions.bed`
```
			NC_000017.10	0	50	0.00
			NC_000017.10	50	100	0.00
			NC_000017.10	100	150	0.00
			NC_000017.10	150	200	0.00
			NC_000017.10	200	250	0.00
			NC_000017.10	250	300	0.00
			NC_000017.10	300	350	0.00
			NC_000017.10	350	400	0.00
			NC_000017.10	400	450	0.00
			NC_000017.10	450	500	0.00
```
This output-file was produced by the following command:

`mosdepth --by 50 sample-output mapt.NA12156.altex.bam`

I thought the `--by` command was supposed to search for the coverage in a specific window size. Since i get only zeros in my output file I was wondering if this `mosdepth --by 50 sample-output mapt.NA12156.altex.bam` was wrong or i didn't understand how exactly this `--by` command works.

So i would like to ask if you could explain me if my output makes sense or if it's incorrect, how exactly i have to use `--by`.

I would like to have an output like this:
```
			NC_000017.10	0	50	1
			NC_000017.10	50	100	2
			NC_000017.10	100	150	15
			NC_000017.10	150	200	5
			NC_000017.10	200	250	7
			NC_000017.10	250	300	0
			NC_000017.10	300	350	38
			NC_000017.10	350	400	12
			NC_000017.10	400	450	4
			NC_000017.10	450	500	1

```
where the last row tells us the number of reads that cover this region in a certain interval specified with 
   `--by`.

greetings taco






