Maintenance Practices
Precision measurement
Read a micrometer from the sleeve (0.5 mm increments) plus the thimble (0.01 mm increments). A vernier calliper with 50 divisions on a 49 mm scale reads to 0.02 mm. Always check the zero before use, use the correct measuring force, and measure at the specified point - a taper or an out-of-round shaft gives a different answer at a different position.
Procedures and standards
Know fits and clearances (clearance, interference, transition), safetying methods (lockwire, cotter pins, tab washers), torque and preload, jacking and trestling, control cable tension, and the NDT methods - visual, dye penetrant, magnetic particle, eddy current, ultrasonic and radiography - with what each can and cannot detect. Also FOD control, lockout/tagout, fluid servicing, and the discipline of working to the AMM rather than from memory.
The traps
Reading the thimble in the wrong direction; assuming dye penetrant finds subsurface flaws (it does not); forgetting that a torque wrench with an extension or adaptor changes the effective length and therefore the applied torque; and mixing up inspection intervals.
Worked example
A vernier: the main scale shows 12 mm and the 8th vernier line aligns. With 0.02 mm per division, the reading is 12 + (8 × 0.02) = 12.16 mm. Rule of thumb: on any precision instrument, confirm the zero, then record every digit the instrument can resolve.