barchart(V3~V1,  data = differences,origin=0,box.ratio=40, lty=0,reference=TRUE,stack=TRUE,par.settings=list (axis.text=list(cex=1.5), axis.line = list(lwd=3)),scales=list(y=list(tick.number=8, rot=90,alternating=1), x=list(at=c(6,18,30,42,54,66,78,90,102,114,126,138,150,162,174,186,198), labels=c("n1996","","","","n2000","","","","n2004","","","","n2008","","","","n2012"),draw=TRUE,tck=1   )))

01/31/1996      -7.3667
02/29/1996       0.9413
03/31/1996       9.3252
04/30/1996       0.3147
05/31/1996       8.8593
06/30/1996      10.0297
07/31/1996       0.64i3
08/31/1996       2.1397
09/30/1996       0.6759
10/31/1996      -1.5579
11/30/1996       2.9493
....             ....
goes to 2012..

|   |   |   |   |   |   |   |
1996            2000          2004 and so on

|||||||||||||||||||||||||||||
    |   |   |   |   |   |   |   |
   1996            2000        2004 and so on

where | indicates tick of size 2 and | is size 1 for example
      |