When we switch from one fund to other then first of all, the present units are converted into rupees and than the converted amount is invested in the new fund and accordingly units are allocated.
E.g.
Bond fund _ NAV Rs. 10 (at the time of investment)
Amount invested Rs. 20000
Unit allocated = 2000
Present NAV for Bond fund = 15 RS.
Value in rupees = 2000 units x 15 RS = RS. 30000/-
Now suppose the investor want to switch from Bond to Secured fund then in that case the above amount of 30000/- will be invested in Secured fund.
Present NAV -Secured fund Rs. 20/-
Unit Allocation would stand after switch over - 1500 units
i.e Rs. 30000/20 = 1500 units
Hope the above illustration is of help.