Mount your power tool vertically in all directions using a spirit level then stick one of these to it and you have a crude but effective visual confirmation.

Jadeshay Mini Bubble Spirit Level,5 Pieces Square Bubble Small Spirit Level Picture Hanging Level Mark Measuring Tools 15mm * 15mm * 40mm
4.0
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1 Pc Circular Bubble Spirit Level, Universal Precision Round Bullseye Level, High Precision Large Horizontal Bubble Cardan Level Horizontal Bubble for...
4.0

Pocket Spirit Level – Horizontal Mini Measuring Tool, Portable Bubble Indicator | Furniture Alignment Gauge, RV Picture Frame Leveler, Precision Layout...