21. 某雷達正使用1.5浬測程(Range Scale)，依據雷達設置標準(IMO Radar performance standard)要求，兩個相同距離之目標，其方位鑑別力(discrimination)不得大於多少度？
(A)1
(B)1.5
(C)2
(D)2.5

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Minimum Range

• With own ship at zero speed, an antenna height of 15 m above the sea level and in calm conditions, a navigational buoy (see table) should be detected at a minimum horizontal range of 40 m from the antenna position and up to a range of 1 nm, without changing the setting of control functions other than the range scale selector.
• Compensation for any range error should be automatically applied for each selected antenna, where multiple antennas are installed.
• Discrimination: Range and bearing discrimination should be measured in calm conditions, on a range scale of 1.5 NM or less and at between 50% and 100% of the range scale selected:
• Range: As per Performance Standards of RADAR, a Radar system should be capable of displaying two-point targets on the same bearing, separated by 40 m in range, as two distinct objects.
• Bearing: The radar system should be capable of displaying two-point targets at the same range, separated by 2.5° in bearing, as two distinct objects.
• Roll and Pitch: The target detection performance of the equipment should not be substantially impaired when own ship is rolling or pitching up to +/-10°.
• Display Range Scales: Range scales of 0.25, 0.5, 0.75, 1.5, 3, 6, 12 and 24 NM should be provided. Additional range scales are permitted outside the mandatory set. Low metric range scales may be offered in addition to the mandatory set. The range scale selected should be permanently indicated on the display.

reference:https://medium.com/@circleofmariners/imo-performance-standards-of-radar-5bd447c94af7