How to write a cursor to compare the values of the rows and columns

What is the value you are trying to compare SampledDate or FurnaceID?

Try using recursive CTE than chosing cursor for this operation.

http://msdn.microsoft.com/en-us/library/ms186243(v=sql.105).aspx

https://www.simple-talk.com/sql/t-sql-programming/sql-server-cte-basics/

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