What are the differences in geometry calculations (shape area and shape length) in ArcGIS Pro and ArcMap when using Python?

[codethemap]

I am working on ArcGIS Pro Python Toolbox.

We have ArcMap Adding developed in c sharp .net and now we are trying to develop it into ArcGIS Pro Python Toolbox.

Tool in ArcMap (Tool has multiple functionality in it, I am adding only necessary info):
User select the line feature on the map and when clicked on calculate button it creates the buffer around the selected line and calculate the shape area and shape length of newly form buffers.

In python toolbox code: I am using buffer analysis function to create buffer for selected line.

arcpy.analysis.Buffer()

For shape area and shape length calculation I am using union of the buffer shape area and shape length.
but after I run the tool the the shape area and shape length calculation have huge difference.

So is there any differences in geometry calculations (shape area and shape length) in ArcGIS Pro and ArcMap?

[DanPatterson]

what are the differences? values?

huge differences probably means that the coordinate systems being used are not the same (one may be using the native coordinate system of the data, the other the coordinate system of the map)