There is a great variety of spelling of the same words and word forms in the runic inscriptions. This is something you cannot find in present-day texts. Obviously, the main reason for this spelling variability is the absence of any spelling standards.

The main goal of this study was to find the factors of the orthographic variability for a number of words. The most frequently occurring word forms (stein, reisti, broður, þenna, eptir, hjalpi etc.) from the memorial runestones of Uppland, Södermanland and Östergötland were studied.

The factors causing orthographic variability can be different in nature. To detect them we have to look at the inscriptions both from the point of view of epigraphy and historical phonetics.

The following reasons (factors) of orthographic variability were detected: insufficient number of signs in the runic alphabet; the appearance of new signs; the position of similar runes next to each other in a word; phonetic changes; dialectal differences; mistakes.

These factors are related to the phonetic and the graphic systems of the language. They are not equally influential, i.e. they cover a different number of word forms, they may have an effect on.

The results of the study are presented in a diagram showing graphically the degree of influence of each factor on each of the studied word form.