Q:

QGis aligning to grid north

My first post here.
I'm designing a map at 500.000 for Italy and with EPSG 3035 or 3034 (Lambert Conical Conformal) I'm still deciding... anyway...
In my map I've several points whose symbol is a sort of "rose of winds" and I need they will remain aligned with the Grid North.
How could I do that? I think I'd have to calculate the angle between the Grid North and True North so I could put its value in a column that Qgis can read as an angle of rotation.
I tried with the formula 
                        γ = arctan [tan (λ - λ0) × sin φ]

but I think there's something wrong coause the symbol doesn't align with the grid.

A:

ok... I searched the web and found this discussion: 
http://www.atpforum.eu/forum/technical-subjects/-061-general-navigation/17210-quid-610226-lambert-conformal
so I've written (all in decimal degree) this: 360 - [(λ - λ0) x sinφ0)]
λ = point of interest's longitude
λ0 = 10 (longitude of EPSG 3034 origin)
φ0 = 52 (latitude of EPSG 3034 origin)
Now I've a more consistent rotation for symbols and they appear parallel to grid.

