diff --git a/CHANGELOG.md b/CHANGELOG.md
index f933b03..b7f9d0c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [4.0.0]
+
+### Added
+
+ - Add an extra PacBio entity attribute - plate_number.
+
 ## [3.0.0]
 
 ### Changed
diff --git a/README.md b/README.md
index d82716f..4bc4462 100644
--- a/README.md
+++ b/README.md
@@ -20,22 +20,37 @@ package implements a Python API. The attributes of objects are sequencing
 platform specific. The generator for the PacBio platform is implemented by the
 `PacBioEntity` class.
 
-Examles of generating IDs for PacBio data:
+Examles of generating IDs for PacBio data from Python code:
 
 ```
-from npg_id_generation.main import PacBioEntity
+from npg_id_generation.pac_bio import PacBioEntity
 
 # from a JSON string via a class method
 test_case = '{"run_name": "MARATHON","well_label": "D1"}'
 print(PacBioEntity.parse_raw(test_case, content_type="json").hash_product_id())
 
 # by setting object's attributes
-print(PacBioEntity(run_name="MARATHON", well_label="D1").hash_product_id()
+print(PacBioEntity(run_name="MARATHON", well_label="D1").hash_product_id())
+print(PacBioEntity(
+    run_name="MARATHON",
+    well_label="D1",
+    plate_number=2
+  ).hash_product_id()
+)
 
 # sample-specific indentifier
 # for multiple tags a sorted comma-separated list of tagscan be used
 print(PacBioEntity(run_name="MARATHON", well_label="D1", tags="AAGTACGT").hash_product_id()
-``` 
+```
+
+The npg_id_generation package also contains a script, `generate_pac_bio_id`,
+which can be called from the command line. The script outputs the generated
+ID to the STDOUT stream. Use the `--help` option to find out details.
+
+```
+# Using the script in the Perl code:
+my $id = `npg_id_generation --run_name 'MARATHON' --well_label 'D1'`;
+```
 
 All generators should conform to a few simple rules:
 
@@ -60,6 +75,15 @@ o5 = PacBioEntity.parse_raw('{"well_label": "l1",  "run_name": "r1"}', content_t
 o6 = PacBioEntity.parse_raw('{"well_label": "l1","run_name": "r1", "tags": null}', content_type="json")
 ```
 
+In addition, to maintain backwards compatibility for PacBio Revio products,
+the following two objects should generate the same ID, meaning that the
+value of 1 for the plate number attribute is disregarded.
+
+```
+o1 = PacBioEntity(run_name="r1", well_label="l1")
+o2 = PacBioEntity(run_name="r1", well_label="l1", plate_number=1)
+```
+
 The algorithm used for generation of identifiers can be replicated in Perl;
-on identical input data it gives identical results. However, we cannot guarantee
-that this parity will always be maintained in future.
+on identical input data it gives identical results. However, we cannot
+guarantee that this parity will always be maintained in future.
diff --git a/bin/generate_pac_bio_id b/bin/generate_pac_bio_id
index 0b7396d..fca5a27 100755
--- a/bin/generate_pac_bio_id
+++ b/bin/generate_pac_bio_id
@@ -23,7 +23,9 @@ import argparse
 from npg_id_generation.pac_bio import PacBioEntity, concatenate_tags
 
 parser = argparse.ArgumentParser(
-    description="Generates a 64 character product id for a pac bio product.",
+    description="""
+    Generates a 64-character product ID for a PacBio sequencing product.
+    """,
     formatter_class=argparse.RawTextHelpFormatter,
 )
 
@@ -36,6 +38,17 @@ parser.add_argument(
     help="The name of the run to which the product belongs.",
 )
 
+parser.add_argument(
+    "-p",
+    "--plate_number",
+    "--plate-number",
+    required=False,
+    type=int,
+    help="""
+Plate number, relevant for Revio instruments only.
+     """,
+)
+
 parser.add_argument(
     "-w",
     "--well_label",
@@ -49,6 +62,7 @@ A well label should fit the pattern A1.
 )
 
 parser.add_argument(
+    "-t",
     "--tag",
     type=str,
     required=False,
@@ -69,7 +83,11 @@ separator = ","
 
 def main():
     tags = concatenate_tags(args.tag)
-    entity = PacBioEntity(run_name=args.run_name, well_label=args.well_label, tags=tags)
+    entity = PacBioEntity(
+        run_name=args.run_name,
+        plate_number=args.plate_number,
+        well_label=args.well_label,
+        tags=tags)
     print(f"{entity.hash_product_id()}\n")
 
 
diff --git a/npg_id_generation/pac_bio.py b/npg_id_generation/pac_bio.py
index b014519..104d4d6 100644
--- a/npg_id_generation/pac_bio.py
+++ b/npg_id_generation/pac_bio.py
@@ -45,12 +45,31 @@ def concatenate_tags(tags: list[str]):
 class PacBioEntity(BaseModel, extra=Extra.forbid):
     """A PacBio class for product ID generation."""
 
-    # Order the attributes alphabetically, to allow for interoperability
-    # with a possible Perl API.
-    # Alternatively the sorting could be achieved with json.dumps()'s
-    # sort_keys argument. See https://docs.python.org/3/library/json.html#basic-usage
+    """
+      Pydantic's current default is to serialize attributes in the order
+      they are listed. if this behaviour changes, we can restore it by
+      using json.dumps() sort_keys argument, see
+      https://docs.python.org/3/library/json.html#basic-usage
+
+      We are not using this explicit sort for now since it adds to the
+      execution time.
+
+      Order the attributes alphabetically!
+    """
+
     run_name: str = Field(title="Pac Bio run name as in LIMS")
     well_label: str = Field(title="Pac Bio well label")
+    plate_number: int = Field(
+        default=None,
+        ge=1,
+        title="Pac Bio plate number",
+        description="""
+        Plate number is a positive integer and is relevant for Revio
+        instruments only, thus it defaults to None.
+        To be backward-compatible with Revio product IDs generated so far,
+        when the value of this attribute is 1, we reset it to undefined.
+        """,
+    )
     tags: str = Field(
         default=None,
         title="A string representing tag or tags",
@@ -76,6 +95,10 @@ def well_label_conforms_to_pattern(cls, v):
             )
         return v
 
+    @validator("plate_number")
+    def plate_number_default(cls, v):
+        return None if (v is None) or (v == 1) else v
+
     @validator("tags")
     def tags_have_correct_characters(cls, v):
         if (v is not None) and (not re.match("^[ACGT]+(,[ACGT]+)*$", v)):
diff --git a/tests/test_hashing.py b/tests/test_hashing.py
index e3ed46f..835c3d0 100644
--- a/tests/test_hashing.py
+++ b/tests/test_hashing.py
@@ -129,6 +129,75 @@ def test_tags_have_correct_characters():
         )
 
 
+def test_plate_number_validation():
+
+    for n in [-1, 0]:
+        with pytest.raises(ValidationError) as excinfo:
+            PacBioEntity(run_name="MARATHON", well_label="A1", plate_number=n)
+        assert "ensure this value is greater than or equal to 1" in str(excinfo.value)
+
+
+def test_plate_number_defaults():
+    """Test backwards compatibility for the plate number"""
+
+    e1 = PacBioEntity(run_name="MARATHON", well_label="A1", tags="TAGC", plate_number=1)
+    e2 = PacBioEntity(run_name="MARATHON", well_label="A1", tags="TAGC")
+    e3 = PacBioEntity(
+        run_name="MARATHON", well_label="A1", tags="TAGC", plate_number=None
+    )
+    assert e1.plate_number is None
+    assert e2.plate_number is None
+    assert e3.plate_number is None
+    assert e1.json(exclude_none=True) == e2.json(exclude_none=True)
+    assert e1.json(exclude_none=True) == e3.json(exclude_none=True)
+    assert e1.hash_product_id() == e2.hash_product_id()
+    assert e1.hash_product_id() == e3.hash_product_id()
+
+    e1 = PacBioEntity(run_name="MARATHON", well_label="A1", plate_number=1)
+    e2 = PacBioEntity(run_name="MARATHON", well_label="A1")
+    assert e1.plate_number is None
+    assert e2.plate_number is None
+    assert e1.json() == e2.json()
+    assert e1.hash_product_id() == e2.hash_product_id()
+
+
+def test_multiple_plates_make_difference():
+
+    id_1 = PacBioEntity(
+        run_name="MARATHON", well_label="A1", tags="ACGT"
+    ).hash_product_id()
+    id_2 = PacBioEntity(
+        run_name="MARATHON", well_label="A1", tags="ACGT", plate_number=2
+    ).hash_product_id()
+    id_3 = PacBioEntity(
+        run_name="MARATHON", well_label="A1", tags="ACGT", plate_number=3
+    ).hash_product_id()
+    assert id_1 != id_2
+    assert id_3 != id_2
+
+    id_1 = PacBioEntity(run_name="MARATHON", well_label="A1").hash_product_id()
+    id_2 = PacBioEntity(
+        run_name="MARATHON", well_label="A1", plate_number=2
+    ).hash_product_id()
+    id_3 = PacBioEntity(
+        run_name="MARATHON", well_label="A1", plate_number=3
+    ).hash_product_id()
+    assert id_1 != id_2
+    assert id_3 != id_2
+
+    json = PacBioEntity(run_name="MARATHON", well_label="A1", plate_number=2).json(
+        exclude_none=True
+    )
+    assert json == '{"run_name": "MARATHON", "well_label": "A1", "plate_number": 2}'
+    json = PacBioEntity(
+        run_name="MARATHON", well_label="A1", tags="ACTGG", plate_number=2
+    ).json(exclude_none=True)
+    assert (
+        json
+        == '{"run_name": "MARATHON", "well_label": "A1", "plate_number": 2, "tags": "ACTGG"}'
+    )
+
+
 def test_expected_hashes():
     """Test against expected hashes."""