been quite a few unusual-to-the-modern-eye keyboards floating by the tl this morning, so here’s a contribution. this type of fully mechanical adding machine would ordinarily run up to nine for every place, but since every key press just adds its value anyway, there’s no difference between pressing ‘8’ once or ‘4’ twice. my understanding is that the latter was often preferred, even on full-size models, for efficiency. so these compact units were ultimately a bit of a no-brainer!