Tektronix 2247A Operator's Manual page 221

Performance Check Procedure
e. CHECK—the readout Is 0.000 V +0.005 V and the GND cursor Is
aligned with the bottom of the signal.
f. Set trigger level cursor to align with the top of the signal.
g. CHECK—the readout is between 0.475 V and 0.525 V.
h. Press CLEAR DISPLAY.
J. Disconnect test equipment If ending here.
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