diff --git a/scouter/utils/clients/pi_web_api_client.py b/scouter/utils/clients/pi_web_api_client.py
index 3ad5c67..a8ba79a 100644
--- a/scouter/utils/clients/pi_web_api_client.py
+++ b/scouter/utils/clients/pi_web_api_client.py
@@ -287,15 +287,18 @@ class PIWebAPIClient(SientiaMonitoring):
 
         # Build query parameters with WebIds (filtering out None values)
         params: list[tuple[str, str]] = [('webid', web_id['webid']) for web_id in web_ids.values()]
+        # Invert startTime and endTime to get descending order (most recent first)
+        # PI Web API returns descending order when endTime < startTime
         params.extend(
             [
-                ('startTime', start_time),
-                ('endtime', end_time),
+                ('startTime', end_time),  # Use end_time as startTime (inverted)
+                ('endtime', start_time),  # Use start_time as endTime (inverted)
                 ('selectedFields', 'Items.Name;Items.Items.Timestamp;Items.Items.Value'),
             ]
         )
 
-        params.append(('maxCount', str(max_count)))
+        if max_count is not None:
+            params.append(('maxCount', str(max_count)))
 
         data = await self._curl_get_json(
             url=url,
diff --git a/tests/activities/test_api.py b/tests/activities/test_api.py
index 77810aa..8bd21e8 100644
--- a/tests/activities/test_api.py
+++ b/tests/activities/test_api.py
@@ -146,7 +146,7 @@ async def test_get_tag_values_success(api_activity):
 
     assert len(result) == 3
     assert result[0]['name'] == 'tag1'
-    assert result[0]['value'] == 10.5
+    assert result[0]['value'] == pytest.approx(10.5)
     assert result[1]['name'] == 'tag2'
     assert result[2]['name'] == 'tag3'
     assert result[0]['timestamp'] == '2023-01-01 12:02:00+0000'
@@ -332,6 +332,6 @@ async def test_get_tag_values_with_nan_values(api_activity):
 
     # Verify
     assert len(result) == 2
-    assert result[0]['value'] == 10.0
+    assert result[0]['value'] == pytest.approx(10.0)
     # NaN should be preserved in the result
     assert pd.isna(result[1]['value'])
diff --git a/tests/utils/clients/test_pi_web_api_client.py b/tests/utils/clients/test_pi_web_api_client.py
index 7c897e3..f4f8870 100644
--- a/tests/utils/clients/test_pi_web_api_client.py
+++ b/tests/utils/clients/test_pi_web_api_client.py
@@ -164,28 +164,28 @@ def test_extract_numeric_with_float(pi_client):
     """Test extracting numeric value from float"""
     result = pi_client._extract_numeric(42.5)
 
-    assert result == 42.5
+    assert result == pytest.approx(42.5)
 
 
 def test_extract_numeric_with_int(pi_client):
     """Test extracting numeric value from int"""
     result = pi_client._extract_numeric(42)
 
-    assert result == 42.0
+    assert result == pytest.approx(42.0)
 
 
 def test_extract_numeric_with_string(pi_client):
     """Test extracting numeric value from string"""
     result = pi_client._extract_numeric('123.45')
 
-    assert result == 123.45
+    assert result == pytest.approx(123.45)
 
 
 def test_extract_numeric_with_dict(pi_client):
     """Test extracting numeric value from dictionary"""
     result = pi_client._extract_numeric({'Value': 99.9})
 
-    assert result == 99.9
+    assert result == pytest.approx(99.9)
 
 
 def test_extract_numeric_with_invalid_value(pi_client):
@@ -436,9 +436,9 @@ async def test_get_latest_values_df_with_custom_params(mock_curl_get_json, pi_cl
     call_args = mock_curl_get_json.call_args
     params = call_args[1]['params']
 
-    # Verify parameters
-    assert ('startTime', '*-7d') in params
-    assert ('endtime', '*-1d') in params
+    # Verify parameters (inverted: startTime uses end_time, endTime uses start_time)
+    assert ('startTime', '*-1d') in params
+    assert ('endtime', '*-7d') in params
     assert ('maxCount', '100') in params
     assert call_args[1]['timeout'] == 60
     assert call_args[1]['metadata'] == metadata
@@ -558,3 +558,31 @@ async def test_get_latest_values_df_default_max_count(mock_curl_get_json, pi_cli
     params = call_args[1]['params']
 
     assert ('maxCount', '1') in params
+    # Verify default time parameters are inverted (startTime uses end_time default, endTime uses start_time default)
+    assert ('startTime', '*') in params  # Default end_time
+    assert ('endtime', '*-1d') in params  # Default start_time
+
+
+@pytest.mark.asyncio
+@patch.object(PIWebAPIClient, '_curl_get_json', new_callable=AsyncMock)
+async def test_get_latest_values_df_with_none_max_count(mock_curl_get_json, pi_client):
+    """Test get_latest_values_df does not send maxCount parameter when max_count is None"""
+    mock_curl_get_json.return_value = {'Items': []}
+
+    web_ids = {'tag1': {'webid': 'webid1'}}
+
+    await pi_client.get_latest_values_df(
+        web_ids=web_ids,
+        endpoint='/streamsets/recorded',
+        max_count=None,
+    )
+
+    call_args = mock_curl_get_json.call_args
+    params = call_args[1]['params']
+
+    # Verify maxCount parameter is not present when max_count is None
+    assert ('maxCount', '1') not in params
+    assert ('maxCount', None) not in params
+    # Verify time parameters are still present
+    assert ('startTime', '*') in params
+    assert ('endtime', '*-1d') in params