Determination of tax - stay and appellate delays exclude limitation, with hearing rights and adjusted interest and penalties. Periods of stay or appellate delay are excluded from computing limitation for reassessment. If an allegation of fraud or willful suppression in a notice is rejected on appeal, the proper officer must determine tax under ordinary assessment procedures. Officers must issue appellate-directed orders within a statutory period, state reasons, confine demands to notice grounds, and modify interest and penalty when tax is altered on appeal. Interest on tax shortfalls is payable regardless of mention in the order. Self-assessed unpaid tax and interest are recoverable under recovery provisions, and double penalties for the same act are prohibited.