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.

1 Pc Circular Bubble Spirit Level, Universal Precision Round Bullseye Level, High Precision Large Horizontal Bubble Cardan Level Horizontal Bubble for...
4.0

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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5pcs Plastic Cylindrical Small Bubble Level Vials Photo Mini Spirit Leveling Gauge Picture Hanging Level Tool
4.0