Lead aVR is closest to being isoelectric (slightly more positive than negative)

The two perpendiculars are -60 ^o and +120 ^o.

Lead I is mostly negative; lead III is mostly positive.

Therefore the axis is close to +120 ^o. Because aVR is slightly more positive, the axis is slightly beyond +120 ^o (i.e., closer to the positive right arm for aVR).