The index value of a smallcase indicates the absolute price returns of that particular smallcase from the date of its inception or date of investment:
For uninvested smallcases, the index value on the inception date of the smallcase would be 100. The current index value shows by how much it has gone up since then due to market movement
For invested smallcase the index value represents the P/L since date of investment. On the day the day of investment the value is 100 and any movement thereon represents the % returns
By hovering over the index value you can view the daily percentage increase or decrease.