Tech

Perceptual Neutral:

hue 245, chroma 0.002. Tiny cool tint to counter the warm bias most monitors have at low brightness. Apple-HIG trick — looks like pure gray on your screen.

Based on Racket like python but with contracts (controlling types and tests etc)

exiftool -time:all -a -G1 "/Users/jonas/Downloads/sth.pdf"

The ultra sound will generate mini bubbles cleaning the items

Lower frequency generates bigger bubbles and cleans stronger. Higher frequencies are more gentle but cleans less well 40-60kHz is a good range

If there are airholes or fractures, it might damage the item

Do Not Clean:

• Emeralds, Opals, Pearls, Coral, Amber, Turquoise, Lapis lazuli, Malachite, Onyx, Tanzanite, Moonstone, Zircon

• Glued gems, Ultrasonics can loosen adhesives, Stones with fracture filling, oiling, or dyeing, Heat-sensitive gems

Need at least 7mil QR code. 50W 像素

Taobao 3/5mil, 100W pixel, 73-93mm DOF (depth of field), 380rmb

4 Stars Comet 4/7mil, 50W pixel, 300rmb

5 Stars Comet 3/4mil, 100W pixel, 500rmb