gtk_tree_model_get(model, iter, DIVE_INDEX, &indx, -1);
dive = get_dive(indx);
value = get_weight_units(total_weight(dive), &decimals, NULL);
gtk_tree_model_get(model, iter, DIVE_INDEX, &indx, -1);
dive = get_dive(indx);
value = get_weight_units(total_weight(dive), &decimals, NULL);