-- create a table to store our results
-- create a dummy unique identifier on the table
CREATE TABLE #Counter2
(
   RowNumber INT IDENTITY(1,1)
   ,StartDate DATETIME
   ,[Value] FLOAT
   ,Code CHAR(1)
   ,Counter INT
)

--insert all existing data from original table into our results table
INSERT INTO #Counter2(StartDate, [Value], Code)
SELECT StartDate
   , [Value]
   , Code 
FROM #Counter

-- create a counter variable
-- this will be used to count our rows
DECLARE @Counter INT
SET @Counter = 0

-- this is a dummy variable
-- we need it as an anchor to keep our running total
DECLARE @RowNumber INT

-- now we will set the counter
-- we need to start the counter when the value is between 10 and 15
-- accumulate the counter until we get to 10
-- start again when we get to the next value between 10 and 15

UPDATE #Counter2
SET @Counter = Counter = CASE WHEN (@Counter >= 1 AND @Counter < 10) OR ([Value] >= 10 AND [Value] <=15)
                           THEN @Counter + 1
                           ELSE 0 -- restart the counter
                           END
   ,@RowNumber = RowNumber
FROM #Counter2

-- take a look at our results
SELECT * 
FROM #Counter2

-- clean up
DROP TABLE #Counter2