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BNZ currency strategist Raiko Shareef said most commentary on the alleged intervention suggested a figure in the region of $200 million, which would rank among what had previously been classified as ''passive intervention''.
Any active intervention, such as happened in 2007, would appear at face value to be inconsistent with the Reserve Bank's stated framework.
Specifically, the Reserve Bank had as recently as May last year noted intervention would need to be consistent with monetary policy.
''To the extent one believes the Reserve Bank is in the midst of a broader hiking cycle - as we do - this criteria does not appear to have been met.''
The Reserve Bank might consider itself to have some wriggle room on that point, having declared itself to be in a short-term pause for reflection on interest rates, Mr Shareef said.
Still, without a press statement from the Reserve Bank, which was presented within hours of the first salvo in 2007, he was unsure whether the latest intervention was the start of an extensive campaign like the $2.3 billion sold then.
''More plausible, in our minds, is the idea the Reserve Bank is engaging in what we call passive intervention, where the bank is expressing its long-held view of an overvalued dollar by selling in relatively small volume.''
Since Governor Graeme Wheeler took the helm, the Reserve Bank engaged in such activity in November and December in 2012 and April 2013.
The rules on that type of action were not clear, Mr Shareef said.
Mr Wheeler sounded peeved at the strength of the dollar at the July official cash rate review, invoking intervention language by calling the currency's strength unjustified.
''Even if the bank turned out to have no hand in the price action on Monday morning, we can't imagine Mr Wheeler being displeased.''
The major question to answer was why now?
One answer was the Reserve Bank saw the opportunity to hasten a movement towards more favourable monetary conditions.
The central bank had been worried a return to a more normal level of interest rates had been hindered by a stubbornly strong dollar.
''With the tailwind of a broader US dollar rally, the Reserve Bank might have simply decided to throw its weight behind New Zealand dollar bears for relatively good risk-reward, as they'd be able to take profit in the likely scenario the dollar ends up weaker towards year end,'' he said.