British East Africa (KUT) Stamps: 1890: SG4/7; Used; CV £61.50
Note
The 2.5a stamp has a good example [UR] from the watermark [PURE LINEN WOVE BANK]
The 1 a stamp is on thin paper and includes part of an angled watermark. The letter [D] + part of another letter [B] is visible - see scan + flipped scan. This part of a rare BRADBURY WILKINSON watermark which is only occasionally found on stamps of this issue, e.g.
https://stampauctionnetwork.com/co/co30926.cfm
Shows exactly the same watermark on a 4a stamp.
Most stamps on the sheet had no watermark
The 1a and 2 a stamps have a top or base side imperforate which is a characteristic of stamps from the outer sheet margins of the 1890 issue.