The head of every department and office shall prepare and submit to the City Manager on or before the fifteenth day of February in each year an estimate of the whole cost and expense of providing for and maintaining his office during the ensuing fiscal year, which estimate shall be in detail, and such other information as may be required by the City Manager for use by the City Manager in preparing his proposed budget for submission to the City Council. Each department head may require the head of any division in his department to prepare similar estimates of the cost and expense of maintaining such division for use in preparing departmental estimates.