Question about how to degree my cam

I'm familiar how to do it but what does the - (minus) sign means on when intake opens at 0.050?
The cam card says -1.5, should I degree it 1.5 degree BTDC or is it 1.5 ATDC as there's a minus sign?
The most cam I've been in touch with use to be degree 7-8 degree (without a minus sign) BTDC, never seen this -1.5 degree before

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