Before April 30 of each fiscal year (or an earlier date fixed by the budget officer), each department head shall transmit to the budget officer the budget requests and revenue estimates for his department for the budget year. The budget request shall be an estimate of the financial requirements of the department for the budget year, and shall be made in such form and detail, with such supporting information and justifications, as the budget officer may prescribe. The revenue estimate shall be an estimate of all revenues to be realized by department operations during the budget year. At the same time, the finance officer or department heads shall transmit to the budget officer a complete statement of the amount expended for each category of expenditure in the budget ordinance of the immediately preceding fiscal year, a complete statement of the amount estimated to be expended for each category of expenditure in the current year’s budget ordinance by the end of the current fiscal year, the amount realized from each source of revenue during the immediately preceding fiscal year, and the amount estimated to be realized from each source of revenue by the end of the current fiscal year, and such other information and data on the fiscal operations of the local government or public authority as the budget officer may request. (1927, c. 146, s. 5; 1955, cc. 698, 724; 1971, c. 780, s. 1.)