In that case instead of adding up all of the delta's it would be more accurate to:

1. Determine the altitudes of all local minima and maxima of elevations.
1a. I would smooth the data first, but that's not necessarily required
1b. Just graph the elevations and choose the tops of humps and bottom of valleys

2. Sum local maxima minus the sum of local minima
2a. the same number of each
2b. start from a local minimum if we're interested in amount climbed.

local maximum is the point where the ride shifts from going up to going down, and vice versa for the minimum.

Adding the deltas is OK if that's all the information you have, but it will always build up errors from rounding and measurement variations, especially when it's already smoothed (such as the .4m increments).