Deferment of advance tax on periodic commission receipts allowed, with notification and interest if deferred payment is not made promptly. Where part of advance-taxable income comprised periodically receivable commission not received or adjusted before instalments became due, the assessee could defer advance tax on that part until the date the income was normally received or adjusted, provided the assessee communicated the deferred date to the Income-tax Officer; failure to pay within a short period after receipt or adjustment attracted simple interest from the date of receipt or adjustment to the date of payment.