Equip only as a sorcery

[Curious penguin]

How can I put a +1/+1 counter on a creature equipped with ring of xathrid if it's equipped only as a sorcery? I thought that means you can only equip it when the stack is empty. Then the ring isn't equipped after that turn like a sorcery?

[Poof]

Once something is equipped it stays that way until you unequip or the creature dies