How far out or in should a tuning slide be on a trumpet?

Question

because mine is about 3 cm. out, but it doesn't sound right when i play a Bb scale. i dont know if its flat or sharp, but yeah.

(Bb trumpet)

Answer 1

the slide should be out just anof so it's the right pitch keep on trying or go on http://www.metronomeonline.com/ and click on  A440 and it will play a note try to mach it  

Answer 2

Test the tones against those of a piano.