Worked both in the round and flat.

There is an errata for this pattern
After the instructions These 4 rounds form the twist rib patt. it should say:

Repeat these last 4 rounds 5 times more.

After divide for thumbhole and the 6th line down reads: Change to yarn A. It should say:
Change to yarn B
If you need any help please don’t hesitate to contact me, Jane Ellison