Hi Selva,
That's an interesting cover.

It looks as though it was posted from Aarau without a stamp (or the stamp fell off) so the postage due stamp was applied (10c to pay as double the usual rate of 5c).
It was sent to the village of Leutwyl in the same canton of Aargau. I see the name of this village is now spelled "Leutwil".
I collect post cards from the Swiss village of Wilderswil near Interlaken and I can see a similar change of spelling from "Wilderswyl" in the cards at around the start of the 20th century.
There are three versions of this postage due stamp design based on the shape of the corner triangles:
Type I has the edge of the triangle in the top right corner of the stamp nearest the centre of the stamp complete. The other three triangles also have complete edges without breaks.
Type II has this edge of the triangle in the top right corner broken and this also occurs with the frame inverted where its the corresponding edge of the triangle in the bottom left corner that's broken.
If you look carefully at your stamp you'll see that you have an example of type II with the inverted frame, i.e. the triangle in the bottom left hand corner of the stamp has a broken frame.
Both forms of the Type II frame exist on both the white paper and granite paper issues. The frame types don't make much difference to the catalogue prices except for some of the higher values in the set.
All the best,