diff --git a/nvitop/api/collector.py b/nvitop/api/collector.py
index 9467487..ea81578 100644
--- a/nvitop/api/collector.py
+++ b/nvitop/api/collector.py
@@ -855,9 +855,10 @@ class _StatisticsMaintainer:  # pylint: disable=missing-class-docstring,missing-
         self.last_timestamp = timestamp
 
     def mean(self) -> float:
+        if self.integral is None:
+            return math.nan
+
         if self.has_nan:
-            if self.integral is None:
-                return math.nan
             return self.integral / (self.last_timestamp - self.start_timestamp)
 
         timestamp = timer()
@@ -865,12 +866,12 @@ class _StatisticsMaintainer:  # pylint: disable=missing-class-docstring,missing-
         return integral / (timestamp - self.start_timestamp)
 
     def min(self) -> float:
-        if self.has_nan or self.min_value is None:
+        if self.min_value is None:
             return math.nan
         return self.min_value
 
     def max(self) -> float:
-        if self.has_nan or self.max_value is None:
+        if self.max_value is None:
             return math.nan
         return self.max_value
 
diff --git a/nvitop/api/process.py b/nvitop/api/process.py
index 1f451c7..d164579 100644
--- a/nvitop/api/process.py
+++ b/nvitop/api/process.py
@@ -452,10 +452,10 @@ class GpuProcess:  # pylint: disable=too-many-instance-attributes,too-many-publi
 
     _pid: int
     _host: HostProcess
-    _ident: tuple
     _device: Device
-    _hash: int | None
     _username: str | None
+    _ident: tuple
+    _hash: int | None
 
     # pylint: disable-next=too-many-arguments
     def __new__(
diff --git a/nvitop/api/utils.py b/nvitop/api/utils.py
index d420ffe..f9890ea 100644
--- a/nvitop/api/utils.py
+++ b/nvitop/api/utils.py
@@ -506,7 +506,7 @@ SIZE_UNITS: dict[str | None, int] = {
     'MB': 1000**2,
     'GB': 1000**3,
     'TB': 1000**4,
-    'PB': 1000**4,
+    'PB': 1000**5,
 }
 """Units of storage and memory measurements."""
 SIZE_PATTERN: re.Pattern = re.compile(
@@ -694,9 +694,7 @@ class Snapshot:
         """Support ``for name in snapshot`` syntax and ``*`` tuple unpack ``[*snapshot]`` syntax."""
 
         def gen() -> Generator[str, None, None]:
-            for name in self.__dict__:
-                if name not in ('real', 'timestamp'):
-                    yield name
+            yield from (name for name in self.__dict__ if name not in ('real', 'timestamp'))
 
         return gen()