How is sequencing saturation calculated

[Liripo]

I checked the 10x calculation https://kb.10xgenomics.com/hc/en-us/articles/115003646912-How-is-sequencing-saturation-calculated and I wrote the following code, but the calculation results are different from those of STARsolo：

import pysam
import polars as pl

with pysam.AlignmentFile("Aligned.sortedByCoord.out.bam") as bam:
    cbs = []
    ubs = []
    gxs = []
    dup = []
    for line in bam:
        if line.is_unmapped:
            continue
        cbs.append(line.get_tag("CB"))
        ubs.append(line.get_tag("UB"))
        gxs.append(line.get_tag("GX"))
        dup.append(line.is_duplicate)
    df = pl.DataFrame({
        "CB": cbs,
        "UB": ubs,
        "GX": gxs,
        "dup": dup
    })


duplicate_reads = sum(df['dup'] == True)

unique_confidently_mapped_reads = (
    df.filter(pl.col('CB') != "-",pl.col('GX') != "-")
    [:,['CB','UB','GX']].unique()
).height

1 - unique_confidently_mapped_reads / (unique_confidently_mapped_reads + duplicate_reads)

I want to ask where I went wrong