[agraham]

It's a transparency issue. Because RotateHQ achieves the higher quality by a weighted interpolation of the colours of the four original pixels that cover the block where the rotated pixel is to be positioned and because the colour values are integers and the weighting factors are not there will be a final rounding effect on the final colour value. In this case that is varying the needle background colour from the transparent value that you are using.

In this case you could minimise the effect by chopping off the white extension to the needle on the bitmap and calulating an appropriate x and y offset to position the rotated needle at the centre of the dial. Using a less obvious transparent colour, such as mid-grey, might also be beneficial.