The decrease of the decimal rate -1.05 mm/year can be rounded to -1. You don’t need to round 2.48 because you’re multiplying by -1. Since -1.05 is negative and rounded to a greater value, the estimate could be adjusted to a slightly lesser value, maybe -2.5 or -2.6.
Round 1.05 mm to the nearest whole number the result is -1.1 then round 2.48 which the result will be equal to 3. The total variation in water level is -3.3
