diff --git a/resources/function_help/json/$area b/resources/function_help/json/$area
index 3c96aa9b708..fb15461a32f 100644
--- a/resources/function_help/json/$area
+++ b/resources/function_help/json/$area
@@ -1,6 +1,6 @@
 {
   "name": "$area",
   "type": "function",
-  "description": "Returns the area of the current feature.",
+  "description": "Returns the area of the current feature. The area calculated by this function respects both the current project's ellipsoid setting and area unit settings. Eg, if an ellipsoid has been set for the project then the calculated area will be ellipsoidal, and if no ellipsoid is set then the calculated area will be planimetric.",
   "examples": [ { "expression":"$area", "returns":"42"}]
 }
diff --git a/resources/function_help/json/$length b/resources/function_help/json/$length
index a7aad15a9b7..74dc20cac2b 100644
--- a/resources/function_help/json/$length
+++ b/resources/function_help/json/$length
@@ -1,7 +1,7 @@
 {
   "name": "$length",
   "type": "function",
-  "description": "Returns the length of a linestring. If you need the length of a border of a polygon, use $perimeter instead.",
+  "description": "Returns the length of a linestring. If you need the length of a border of a polygon, use $perimeter instead. The length calculated by this function respects both the current project's ellipsoid setting and distance unit settings. Eg, if an ellipsoid has been set for the project then the calculated length will be ellipsoidal, and if no ellipsoid is set then the calculated length will be planimetric.",
   "examples": [
 	{ "expression":"$length", "returns":"42.4711"}
   ]
diff --git a/resources/function_help/json/$perimeter b/resources/function_help/json/$perimeter
index 64a3a5765e8..cc1aec52aa8 100644
--- a/resources/function_help/json/$perimeter
+++ b/resources/function_help/json/$perimeter
@@ -1,7 +1,7 @@
 {
   "name": "$perimeter",
   "type": "function",
-  "description": "Returns the perimeter length of the current feature.",
+  "description": "Returns the perimeter length of the current feature. The perimeter calculated by this function respects both the current project's ellipsoid setting and distance unit settings. Eg, if an ellipsoid has been set for the project then the calculated perimeter will be ellipsoidal, and if no ellipsoid is set then the calculated perimeter will be planimetric.",
   "examples": [ { "expression":"$perimeter", "returns":"42"}
   ]
 }
diff --git a/resources/function_help/json/area b/resources/function_help/json/area
index f7f23fa7305..08e01c14235 100644
--- a/resources/function_help/json/area
+++ b/resources/function_help/json/area
@@ -1,7 +1,7 @@
 {
   "name": "area",
   "type": "function",
-  "description": "Returns the area of a geometry polygon object. Calculations are in the Spatial Reference System of this geometry.",
+  "description": "Returns the area of a geometry polygon object. Calculations are always planimetric in the Spatial Reference System (SRS) of this geometry, and the units of the returned area will match the units for the SRS. This differs from the calculations performed by the $area function, which will perform ellipsoidal calculations based on the project's ellipsoid and area unit settings.",
   "arguments": [ {"arg":"geometry","description":"polygon geometry object"}],
   "examples": [ { "expression":"area(geom_from_wkt('POLYGON((0 0, 4 0, 4 2, 0 2, 0 0))'))", "returns":"8.0"}]
 }
diff --git a/resources/function_help/json/length b/resources/function_help/json/length
index 4667fbe3e1c..3a965c32283 100644
--- a/resources/function_help/json/length
+++ b/resources/function_help/json/length
@@ -9,7 +9,7 @@
       "examples": [ { "expression":"length('hello')", "returns":"5"} ] },
       {
       "variant": "Geometry variant",
-      "variant_description": "Calculate the length of a geometry line object. Calculations are in the Spatial Reference System of this geometry.",
+      "variant_description": "Calculate the length of a geometry line object. Calculations are always planimetric in the Spatial Reference System (SRS) of this geometry, and the units of the returned length will match the units for the SRS. This differs from the calculations performed by the $length function, which will perform ellipsoidal calculations based on the project's ellipsoid and distance unit settings.",
       "arguments": [ {"arg":"geometry","description":"line geometry object"}],
       "examples": [ { "expression":"length(geom_from_wkt('LINESTRING(0 0, 4 0)'))", "returns":"4.0"}]
   }]
diff --git a/resources/function_help/json/perimeter b/resources/function_help/json/perimeter
index acdebfdd97c..191927ad4cd 100644
--- a/resources/function_help/json/perimeter
+++ b/resources/function_help/json/perimeter
@@ -1,7 +1,7 @@
 {
   "name": "perimeter",
   "type": "function",
-  "description": "Returns the perimeter of a geometry polygon object. Calculations are in the Spatial Reference System of this geometry.",
+  "description": "Returns the perimeter of a geometry polygon object. Calculations are always planimetric in the Spatial Reference System (SRS) of this geometry, and the units of the returned perimeter will match the units for the SRS. This differs from the calculations performed by the $perimeter function, which will perform ellipsoidal calculations based on the project's ellipsoid and distance unit settings.",
   "arguments": [ {"arg":"geometry","description":"polygon geometry object"}],
   "examples": [ { "expression":"perimeter(geom_from_wkt('POLYGON((0 0, 4 0, 4 2, 0 2, 0 0))'))", "returns":"12.0"}]
 }