Thank you PatriceJ for this clarification. I had a post rejected from a moderator partly because I used a png-file, and therefore I got nervous not to do anything wrong again. I have placed the post again, and I think the moderator accepted my post this time without issues.
I now upload this diagram here too. The size of the diagram is 1119x653 pixels and the file size is 46 kB. When this post is shown, the diagram is reduced in size to about 600 pixels in width in order to be in line with the text frames of QB. The diagram is readable but the text get quite small. However you are able to right click on the the graphics and chose to display the full size diagram in new window. So this works very nice.
However in the FAQ instructions, I find this text: "If you have uploaded an image as an attachment, you can click the arrow next to the 'Attachment Icon' and select it from the list. This will be inserted into your post and can be located where you want it displayed." I do see an icon next to the name of my uploaded file, and I have tried to drag it into the text. But I cannot make this work, and the diagram is not displayed - only the small icon. Therefore I have inserted the picture here by use of the normal picture icon on the functions bar, and the HTML adress for the uploaded diagram produced by QB.
In your post I do not see the PNG-file as an attahed Thumbnail below the post. So it seems I miss some information here regarding how to use this arrow function.