Thanks once again. By no means I do intend to be finicky about this topic. I don't think making the ovals a bit bigger or smaller will make a big difference. What I would like to know is the expected overall size of the letters. I am using standard European grid paper (Rhodia pads and similar stuff) which has 0,5 cm squares. This means that two lines of this paper (which is the common use) have a measurement very close to a 3/8 inches lined paper. As the proportion of BW letters follows the tradition of Spencerian, you have to divide this space in three parts, which gives about 3mm for normal letters without ascenders or descenders. But this is in the case you use the whole space between lines. One should write considerable smaller to avoid the collision of ascenders and descenders in two consecutive lines. I just don't know how to do my practice. I usually use two squares (1 cm) as a maximal height of my letters (for capitals and ascenders) but I write one line every three squares (I skip one square to avoid the collision between lines). I don't know how to explain it in a better way. Hope it makes any sense. Anyway I have the feeling that my writing is bigger than expected.

However, the more I dive into the question the most mysterious I find it. In his Lessons in Practical Penmanship H.P. Beheresmeyer says: "It is advisable that one use a good quality of paper size 8" by 11" with *standard ruling*" (pag. 3). And on the other hand, in his Modern Business Penmanship, Mills (who continuously refers to the blue lines as a reference of measurement) doesn't find necessary to mention any lines in his description of the desired paper for practice ("Good foolscap paper, having rather a smooth surface, is best for this work"; at the very start of his method, which is unpaged).