Where is my Height Gauge?

Material list for that coupler installation:

Drill & #51 drill bit
Pin Vise & 2-56 tap
2-2-56 screws
KD HO coupler height gauge
A section of HO gauge track for testing height of coupler

Where is my height gauge? Drats! It is not where I thought it was. I really do need to get organized...

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