This means you can make numerous small guiding mistakes without affecting the photograph. Piggybacking provides just the type of practice you need to gain experience for other, more difficult forms of astrophotography. Simply keep a bright guidestar centered in it as best you can judge. For photography at longer focal lengths, you need an eyepiece with an illuminated reticle or cross hairs. Dozens of guiding eyepieces are on the market, and many perform other functions as well.
Some people feel that the best design is still the old-fashioned plain cross hairs.
Any motion is revealed when the star emerges from behind their intersection. Some astrophotographers like to keep the star in view, tucked in a corner adjacent to the intersection. If you use a double or dual cross hair, the guidestar can be placed at any of the four intersection points or defocused to nearly fill the small central square. Another approach is to use an eyepiece reticle with concentric circles, each denoting a different guiding tolerance. If you can keep the star inside the appropriate circle, you know that all is well.