The volume/capacity that can be measured by Hutchison's spirometer is:

The volume that remains in the lung even after maximum forceful expiration is residual volume (RV). Since it does not come out into the spirometer, it can not be measured by the conventional spirometry (performed on Hutchison's spirometer). Any capacity that includes RV therefore can not be detected by spirometry. Thus, FRC (ERV + RV) and TLC (TV + IRV + ERV + RV) can not measured directly by spirometry. Hence, the answer is ERV, which can be measured directly by spirometry.