I created a little support tool to get perfect aligned rows of holes in the walls.
For example, if you want to start from the left side of the wall, apply the jig on the left and upper ledges of the wall. Then drill the first hole (88 mm) through the jig. Leave the jig in place and put a M3 screw through the jig into the new drilled hole. Now you can drill the next hole (distance 90 mm), also see drawing.
The end stop is made for walls with a thickness of 3 mm or more.
You can do the same from the other side (right ledge).
The jig is made for M3 screws. You also can increase the holes in the jig to 4 mm and insert a brass tube (4,0mm x 3,2mm x 0,4mm, length 5mm). This will increase the mechanical resistance of the holes in the jig.
You also can use the the 5 mm edges of the jig as a stencil for filing the edges of the walls.