find_scale(): better document why we use powers of 10

src/img2pdf.py

@@ -2147,7 +2147,11 @@ def get_fixed_dpi_layout_fun(fixed_dpi):
 
 def find_scale(pagewidth, pageheight):
     """Find the power of 10 (10, 100, 1000...) that will reduce the scale
-    below the PDF specification limit of 14400 PDF units (=200 inches)"""
+    below the PDF specification limit of 14400 PDF units (=200 inches).
+    In principle we could also choose a scale that is not a power of 10.
+    We use powers of 10 because numbers in the PDF format are represented
+    in base-10 and using powers of 10 will thus just shift the comma and
+    keep the numbers easily readable by humans as well."""
     from math import log10, ceil
 
     major = max(pagewidth, pageheight)

src/img2pdf_test.py

@@ -2211,13 +2211,7 @@ def gif_animation_img(tmp_path_factory, tmp_normal_png, tmp_inverse_png):
     )
     # make sure all frames have the same palette by using -remap
     subprocess.check_call(
-        CONVERT
-        + [
-            str(tmp_img),
-            "-strip",
-            "-remap", str(pal_img),
-            str(in_img)
-        ]
+        CONVERT + [str(tmp_img), "-strip", "-remap", str(pal_img), str(in_img)]
     )
     pal_img.unlink()
     tmp_img.unlink()