Understanding Lag()

Hi,

I have 2 rules as follows

Rule 1:

LagSales = lag(WPSales)

Rule 2:

BuildRatio = if (LagSales ==  0, 1, WPSales/LagSales)

WPSales = BuildRatio*LagSales

The base intx of these measures are week_skup_chnl. BuildRatio has a spread of recalc.

I observed that it calculates correctly at week_skup_chnl.However when I view at month_skup_chnllevel, the values are incorrect.

For eg, the sales for month 1 is 3300 and for month 2 its 6600, am expecting a build ratio of 2 for month 2, instead it shows me some other value such as 1.11.

I am expecting the lag to consider previous month (month 1) while calculating the build ratio for month 2.