Merge pull request #84 from AFM-SPM/SylviaWhittle/hotfix-spm-units

Fix: units pm and mm missing from spm_pixel_to_nm_scaling

Author: SylviaWhittle

AFMReader/spm.py

@@ -28,8 +28,10 @@ def spm_pixel_to_nm_scaling(filename: str, channel_data: pySPM.SPM.SPM_image) ->
         Pixel to nm scaling factor.
     """
     unit_dict = {
+        "pm": 1e-3,
         "nm": 1,
         "um": 1e3,
+        "mm": 1e6,
     }
     px_to_real = channel_data.pxs()
     # Has potential for non-square pixels but not yet implimented