TCGemsA good scan takes about a second. A bad one usually comes down to light or glare. These habits fix almost every miss.
Use soft, even light
Daylight from a window or a ceiling light works best. Avoid a single lamp shining straight down on the card: it puts a bright spot on the surface and hides the card number.
Watch out for glare on holos
Holo and reverse holo cards reflect light, which is exactly what makes them hard to read. If you see a white patch on the card in the camera view, tilt the card slightly until it disappears.
Sleeves are fine, toploaders need a tilt
Penny sleeves barely change anything. Thick toploaders and magnetic cases add a second shiny layer, so tilt them a little more, or take the card out for its first scan.
Fill the frame
Hold the phone so the card fills most of the scanner frame, with all four corners visible. The card number at the bottom matters most: it tells the printings apart.
Scanning a stack
Turn on Auto and hold the cards up one after another. TCGems scans each card as soon as it is steady, so you can flip through a pile without tapping the screen. The batch total adds up as you go.
If the match is wrong
Open the card and pick the right printing from the list. Reporting the wrong match from the card page helps us make the scanner better for everyone.