Other forum users out and about have recomended 21T204, but usrecordingmedia.com says to use the 21T404 if recording on 456.

"This Magnetic Reference Laboratory calibration tape is used for standardizing azimuth, equalization and determining the "0" level or sensitivity of your deck. This tape is for the NAB equalization standard at 355 nWb/m level. Used for Quantegy 456, 457, 499 and GP9. Recorded at 7.5 IPS. Six minutes long.

MRL21T404$105.97"

Any feedack on this?

Thanks, Goldenvoice