rel

rel()
rel(col: Expr)
rel(row: Expr, col: Expr)

Return the path of a cell relative to the position of the cell rel is in. In the first form rel(), the path of the current cell will be returned. In the second form rel(col), the path to a cell in the same row, but a different column will be returned. In the third form rel(row, col), the path to a cell in a different row and column will be returned. The row and col arguments must be integers between -255 and 255.

sum(1, ref(rel(-1)))

Add 1 to the value in the column to the left of this formula.