Hi lyes, I guess I'm not sure I understand - you previously wrote:

> just small grey or black cross is good enough

You should already be seeing a small gray cross. It will show up if you get your mouse in the general area of the center point, the default is that markers are displayed for snap points within 100 pixels of your mouse.

You can adjust the radius if you want inside of moi.ini, under the [Drawing Aids] section, look for this entry:
ObjectSnapMarkerDisplayRadius=100


Here is a screenshot of what you should be seeing with an arc:



That's a small gray cross, right? Are you not seeing those markers yourself?

- Michael