SELECT
  device
  , sum(measurement * num_seconds)
  , max(measurement)
  -- should return 270 as it was the num seconds the measurement was the max of 5
  , last_value(num_seconds) OVER (ORDER BY num_seconds)
FROM (VALUES (1, 4, 6), (1, 4, 270), (1, 5,30), (1, 4, 2640), (1, 3, 654)) t(device, measurement, num_seconds)
GROUP BY 1