One sloka I personally like refer to in order to remind me of spiritual advancement is in the Bhagavad-Gita 2.56.
sthita-dhīr munir ucyate
Word for word:
duḥkheṣu — in the threefold miseries; anudvigna-manāḥ — without being agitated in mind; sukheṣu — in happiness; vigata-spṛhaḥ — without being interested; vīta — free from; rāga — attachment; bhaya — fear; krodhaḥ — and anger; sthita-dhīḥ — whose mind is steady; muniḥ — a sage; ucyate — is called.
One who is not disturbed in mind even amidst the threefold miseries or elated when there is happiness, and who is free from attachment, fear and anger, is called a sage of steady mind.
Is there any passage(s) where Krishna states what is/how to measure spiritual advancement?