LGT FLC MISREADS ALTIMETER. MISSES XING RESTRICTION.

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RECEIVED CLRNC 26 MI E OF KNOX VOR TO CROSS HALIE INTXN AT 11000 FT. HALIE INTXN IS 26 MI W OF KNOX VOR ON THE KNOX 2 ARR CHICAGO. I LEFT FL280 FOR 11000 FT. THE FO ASKED TO LEAVE THE COCKPIT FOR A NATURE CALL AND WAS GRANTED PERMISSION. THIS IS AN OLDER SERIES ACFT WITH THE OLDER ALTIMETERS INSTALLED THAT ARE ANALOG AND HAVE THE HASH MARKS VERSUS THE DIGITAL READOUT ALTIMETERS INSTALLED ON THE ADVANCED SERIES. I LEVELED THE ACFT AT 21000 FT MISREADING THE ALTIMETER BY 10000 FT. THE SO ALSO MISREAD THE ALTIMETER BY 10000 FT. 5 MI E OF HALIE INTXN ATC ASKED WHAT I UNDERSTOOD THE XING ALT TO BE AT HALIE AND I CONFIRMED THE 11000 FT AND IMMEDIATELY SAW MY ERROR AND STARTED FOR 11000 FT. NO CONFLICT WAS INDICATED AND THE CTLR ISSUED A SW HDG FOR DSCNT VECTOR. I HAD NOT BEEN IN THE OLDER TYPE OF ACFT WITH THIS ALTIMETER FOR MORE THAN 2 MONTHS AND I BELIEVE MY MIND STILL ATTUNED TO THE DIGITAL READOUT ON THE ADVANCED MODEL ACFT. ON DSCNT I CHKED THE ALTIMETER SEVERAL TIMES AND NEVER PICKED UP ON THE MISREAD. I CAN ONLY LEARN FROM THIS OCCURRENCE AND STRIVE TO NEVER HAVE THIS HAPPEN AGAIN. IT SEEMS THAT STANDARDIZATION OF INSTRUMENTATION IN THE COCKPIT IS UNATTAINABLE WHEN PITTED AGAINST COST.