Any order placed on smallcase during market hours will be placed at the current market price on your broker platform. Hence, the trades placed on smallcase will, ideally, reflect in your Tradebook.
In smallcase, the ABP or average buy price is calculated as a simple average for accuracy purposes while on your broker - it is calculated using FIFO for tax liability reasons.
Let us take an example to show how the ABP is arrived at on both platforms and how they can differ, despite the trades being the same.
Consider a stock ABC with the following trades placed on a smallcase. The same trades are visible in the tradebook as shown below:
ABP on smallcase:
For the trade placed in January, the first ABP (or ABP during January will be):(800x4)/4 = Rs. 800
Sell orders should not affect the ABP on smallcase, it only affects the qty of shares. So, after the sell trade in March, the qty of shares will be 4-1 =3.
After the buy trade placed in April, the new ABP will be:
(3x800 + 1x1050)/(3+1) = Rs. 862.5
After the sell trade in June, the qty of shares will be 4-1 = 3.
Final ABP after the Buy trade placed in July will be:
(3x862.5 + 1x1100)/(3+1) = Rs. 921.875
This will be the ABP for the stock after September as well unless another buy trade is placed. Only the qty of shares will change after the sell trade in September.
ABP on your broker platform:
The ABP here is calculated using FIFO. So, the sell orders placed in March, June, and September will be deducted starting from the first Buy trades and so on (First In First Out):
ABP: ((4-1-1-1)x800 + 1x1050 + 1x1100))/(4-1+1-1+1-1) = Rs. 983.333
Effect on your investment
The current investment on smallcase will be: qty x ABP = 3 x 921.875 = Rs. 2765.62
and current investment on your broker will be: 3 x 983.333 = Rs. 2949.99
As illustrated, the ABP on smallcase is Rs. 921.875 while on your broker, it is Rs. 983.333 albeit having the same trades - this is due to the different methodologies used in calculating on the two platforms. The values shown in smallcase can be referred to for accuracy.
How does this affect your return?
Your total return (unrealised + realised) will remain the same.
Let's assume that the current price of the stock in the above example is Rs. 1500.
Realised returns = [(1000-800)x1 + (1200-862.5)x1 + (1300-921.875)x1] = 915.625
Unrealised returns = (1500-921.875)x3 = 1,734.375
Total returns = 1,734.375+915.625 = 2,650
On the broker platform:
Realised returns = [(1000-800) + (1200-800) + (1300-800)] = 1,100
Unrealised returns will be = (1500-800) + (1500-1050) + (1500-1100) = 1,550
Total returns = 1,100+1,550 = 2,650