chore: Add transfer bucket working to .md file
diff --git a/erpnext/stock/report/stock_ageing/stock_ageing_fifo_logic.md b/erpnext/stock/report/stock_ageing/stock_ageing_fifo_logic.md
index 9e9bed4..3d759dd 100644
--- a/erpnext/stock/report/stock_ageing/stock_ageing_fifo_logic.md
+++ b/erpnext/stock/report/stock_ageing/stock_ageing_fifo_logic.md
@@ -71,4 +71,39 @@
2nd | -60 | [[-10, 1-12-2021]]
3rd | +5 | [[-5, 3-12-2021]]
4th | +10 | [[5, 4-12-2021]]
-4th | +20 | [[5, 4-12-2021], [20, 4-12-2021]]
\ No newline at end of file
+4th | +20 | [[5, 4-12-2021], [20, 4-12-2021]]
+
+### Concept of Transfer Qty Bucket
+In the case of **Repack**, Quantity that comes in, isn't really incoming. It is just new stock repurposed from old stock, due to incoming-outgoing of the same warehouse.
+
+Here, stock is consumed from the FIFO Queue. It is then re-added back to the queue.
+While adding stock back to the queue we need to know how much to add.
+For this we need to keep track of how much was previously consumed.
+Hence we use **Transfer Qty Bucket**.
+
+While re-adding stock, we try to add buckets that were consumed earlier (date intact), to maintain correctness.
+
+#### Case 1: Same Item-Warehouse in Repack
+Eg:
+-------------------------------------------------------------------------------------
+Date | Qty | Voucher | FIFO Queue | Transfer Qty Buckets
+-------------------------------------------------------------------------------------
+1st | +500 | PR | [[500, 1-12-2021]] |
+2nd | -50 | Repack | [[450, 1-12-2021]] | [[50, 1-12-2021]]
+2nd | +50 | Repack | [[450, 1-12-2021], [50, 1-12-2021]] | []
+
+- The balance at the end is restored back to 500
+- However, the initial 500 qty bucket is now split into 450 and 50, with the same date
+- The net effect is the same as that before the Repack
+
+#### Case 2: Same Item-Warehouse in Repack with Split Consumption rows
+Eg:
+-------------------------------------------------------------------------------------
+Date | Qty | Voucher | FIFO Queue | Transfer Qty Buckets
+-------------------------------------------------------------------------------------
+1st | +500 | PR | [[500, 1-12-2021]] |
+2nd | -50 | Repack | [[450, 1-12-2021]] | [[50, 1-12-2021]]
+2nd | -50 | Repack | [[400, 1-12-2021]] | [[50, 1-12-2021],
+- | | | |[50, 1-12-2021]]
+2nd | +100 | Repack | [[400, 1-12-2021], [50, 1-12-2021], | []
+- | | | [50, 1-12-2021]] |