Uh-oh, your instructor has that look on his face.
You spotted it while walking to the FBO following your instrument proficiency check. You’ve only seen the look twice before: Once after he’d flown a charter plagued by icing and electrical failures, and once after a favorite student choked on a checkride after disputing the designated examiner on some nitpicky definition.
But never has he worn that look after flying with you! A cup of coffee should cheer him up and perhaps move him to note the instrument proficiency check's completion in your logbook.
He drinks the coffee, but says, "Let’s fly again tomorrow."
Then comes a blow-by-blow critique of your flying—especially your navigating, which frankly was pretty awful. Your VOR tracking was marked by constant half-to-three-quarter-scale deflections of the CDI. You never seemed to have the wind nailed; you need more practice before heading off into serious soup.
Serious soup was your plan for tomorrow when flying out of town on vacation. But, point taken. You can do better. Still, you can’t resist mentioning that your flying never exceeded instrument rating practical test tolerances.
"What does that have to do with anything?"
Before you recover from the shock of that rejoinder, he asks, "Was the VOR system checked within the last 30 days?"
Yes, last week, at the airport’s designated checkpoint.
"What was the bearing error?"
Dunno. Didn’t look it up.
"Well, suppose it was the maximum-acceptable 4 degrees. In some scenarios, that error, plus a three-quarter scale deflection of the CDI, could place your aircraft outside a published airway’s primary protected airspace.
"And don’t tell me about the PTS. One of my students got into a big argument with our designated examiner about that."
The look disappears as he opens the Instrument Procedures Handbook to Appendix B and explains: "Some pilots assume that flying to the tolerances set out in the FAA Instrument Practical Test Standards will keep them within protected airspace. As a result, it is important to observe the last sentence of the following note in the PTS: 'The tolerances stated in this standard are intended to be used as a measurement of the applicant's ability to operate in the instrument environment. They provide guidance for examiners to use in judging the applicant's qualifications. The regulations governing the tolerances for operation under Instrument Flight Rules (IFR) are established in 14 CFR Part 91.'"