diff --git a/.github/workflows/mypy-type-check.yml b/.github/workflows/mypy-type-check.yml
index 02befe4d4..987db45ad 100644
--- a/.github/workflows/mypy-type-check.yml
+++ b/.github/workflows/mypy-type-check.yml
@@ -51,3 +51,6 @@ jobs:
           tiatoolbox/models/models_abc.py \
           tiatoolbox/models/architecture/__init__.py \
           tiatoolbox/models/architecture/utils.py \
+          tiatoolbox/wsicore/__init__.py \
+          tiatoolbox/wsicore/wsimeta.py \
+          tiatoolbox/wsicore/metadata/
diff --git a/tiatoolbox/wsicore/metadata/ngff.py b/tiatoolbox/wsicore/metadata/ngff.py
index 464281e36..da99cb3ce 100644
--- a/tiatoolbox/wsicore/metadata/ngff.py
+++ b/tiatoolbox/wsicore/metadata/ngff.py
@@ -9,13 +9,14 @@
 
 from __future__ import annotations
 
-from dataclasses import dataclass, field
 from typing import TYPE_CHECKING, Literal
 
-from tiatoolbox import __version__ as tiatoolbox_version
+if TYPE_CHECKING:
+    from collections.abc import Iterator
 
-if TYPE_CHECKING:  # pragma: no cover
-    from numbers import Number
+from dataclasses import dataclass, field
+
+from tiatoolbox import __version__ as tiatoolbox_version
 
 SpaceUnits = Literal[
     "angstrom",
@@ -169,6 +170,14 @@ class Multiscales:
     datasets: list[Dataset] = field(default_factory=lambda: [Dataset()])
     version: str = "0.4"
 
+    def __iter__(self: Multiscales) -> Iterator:
+        """Iterate over the values of the attributes in the `Multiscales` object.
+
+        Yields:
+            Iterator: An iterator
+        """
+        yield from self.__dict__.values()
+
 
 @dataclass
 class Window:
@@ -186,10 +195,10 @@ class Window:
 
     """
 
-    end: Number = 255
-    max: Number = 255
-    min: Number = 0
-    start: Number = 0
+    end: int = 255
+    max: int = 255
+    min: int = 0
+    start: int = 0
 
 
 @dataclass
diff --git a/tiatoolbox/wsicore/wsimeta.py b/tiatoolbox/wsicore/wsimeta.py
index 97145e5d6..2b1ad6f59 100644
--- a/tiatoolbox/wsicore/wsimeta.py
+++ b/tiatoolbox/wsicore/wsimeta.py
@@ -11,7 +11,7 @@
 
 from numbers import Number
 from pathlib import Path
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, cast
 
 import numpy as np
 
@@ -121,7 +121,7 @@ def __init__(
         self.level_downsamples = (
             [float(x) for x in level_downsamples]
             if level_downsamples is not None
-            else None
+            else [1.0]
         )
         self.level_count = (
             int(level_count) if level_count is not None else len(self.level_dimensions)
@@ -212,7 +212,9 @@ def level_downsample(
         ceil = int(np.ceil(level))
         floor_downsample = level_downsamples[floor]
         ceil_downsample = level_downsamples[ceil]
-        return np.interp(level, [floor, ceil], [floor_downsample, ceil_downsample])
+        return float(
+            np.interp(level, [floor, ceil], [floor_downsample, ceil_downsample])
+        )
 
     def relative_level_scales(
         self: WSIMeta,
@@ -260,13 +262,16 @@ def relative_level_scales(
             [0.125, 0.25, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0]
 
         """
+        base_scale: np.ndarray | float
+        msg: str
+
         if units not in ("mpp", "power", "level", "baseline"):
             msg = "Invalid units"
             raise ValueError(msg)
 
         level_downsamples = self.level_downsamples
 
-        def np_pair(x: Number | np.array) -> np.ndarray:
+        def np_pair(x: Resolution) -> np.ndarray:
             """Ensure input x is a numpy array of length 2."""
             # If one number is given, the same value is used for x and y
             if isinstance(x, Number):
@@ -274,6 +279,7 @@ def np_pair(x: Number | np.array) -> np.ndarray:
             return np.array(x)
 
         if units == "level":
+            resolution = cast("float", resolution)
             if resolution >= len(level_downsamples):
                 msg = (
                     f"Target scale level {resolution} > "
@@ -296,7 +302,7 @@ def np_pair(x: Number | np.array) -> np.ndarray:
             if self.objective_power is None:
                 msg = (
                     "Objective power is None. "
-                    "Cannot determine scale in terms of objective power.",
+                    "Cannot determine scale in terms of objective power."
                 )
                 raise ValueError(
                     msg,