preview orthogonal lines

[d3dac]

Hello.
Can someone help me with this problem?
In practice when I have to draw a rectangle (for example) , after tracking the base and height, if I pointed the cursor on the first vertex of the base, moving the cursor down appeared the green dotted preview of the orthogonal line at the base so you know exactly where to stop me to create the second base exactly the same as the first.
the problem is that this preview is not coming out now, someone can tell me why?

 

[Tristan]

activate object snap point (f11)

 

[d3dac]

Okay, thank you.
I went on tools-->options-->selection-->preview
and I put the spuns

 

[Tristan]

What does that have to do with it? The preview of selections doesn't do what you asked!

:36_9_4:

 

[d3dac]

What does that have to do with it? The preview of selections doesn't do what you asked!

:36_9_4:

but now it works with the snap!
Thank you.

 

[Giuseppe Mauro]

chedo refers to osnap track