Add compression statistics to README

README.md

@@ -19,6 +19,14 @@ This dataset was exported from the **CellxGene Census** as a **chunked + compres
 - **Shape**: `100,000 cells × 61,497 genes`
 - **Zarr path**: `lung.zarr`
 
+### Compression
+
+- **Uncompressed** (dense float32): **22.91 GB**
+- **Compressed Zarr**: **~307 MB** (322 MB on Hub)
+- **Compression ratio**: **~76×** (Blosc zstd on sparse single-cell data)
+
+The high compression ratio is achieved through Blosc zstd compression optimized for sparse expression matrices typical in single-cell RNA-seq data.
+
 ### Included labels
 
 - `obs/cell_type`
@@ -197,13 +205,13 @@ sc.tl.leiden(adata, resolution=0.5)
 
 Measured locally while building this dataset:
 
-- open Zarr group: **0.0012 s**
-- read one `X[chunk]` (1000×1000): **0.0061 s**
+- open Zarr group: **0.0021 s**
+- read one `X[chunk]` (1000×1000): **0.0864 s**
 
 ```json
 {
-  "open_seconds": 0.0011517200618982315,
-  "read_chunk_seconds": 0.006099492311477661,
+  "open_seconds": 0.0021242350339889526,
+  "read_chunk_seconds": 0.08641284704208374,
   "chunk_shape": [
     1000,
     1000