Adjustable sieve means (31) are provided for an agricultural harvesting machine (1) comprising louvres (41) positioned behind one another and being movable through a range of positions between a fully closed and a fully opened position; consecutive louvres defining an opening (d) inbetween when in an opened position; adjustment means (47) for changing said opening (d); and opening indicator means (48), including a movable part (65), which is unitarily moved with one of said louvres (41), when said opening (d) is adjusted.
These indicator means (48) permit the verification of the sieve opening (d), even when the louvres are not accessible for measurement with gauges, and a direct link between the louvres (41) and the movable part (65) avoids the inaccuracies which are conceivable when the indicator means (48) is sensing the movement of further, intermediate components of the adjustment means (47).