bone age computer

looking back on how i used to do maths at school with the log tables and the slide rules which were then replaced about 1980 by chunky calculators with cylon redeye displays thinking of a computer i used in the 1990s the napier bones
napier created a portable calculating machine a line of ten bone rods numbered 0-9 and which you slide together to perform rapid (for the early 17th century ) calculations
for example above 5 X 684 work out out by hand using a quill pen by candlelight or just read off 3420 burn me for a witch! that's magic

the genaille rods did not arive until 1891 and i must admit do not have the fun of playing with my napiers bones which as of course as Genaille and co inspiration edouard lucas said eliminate the complicated need to add on and carry numbers in the single row and with these you follow the triangles starting from the right ie as above 907 X 5 = 4535
however genaille rod is now seen as a mathematical novelty and both work with single digit calculation only
you just buy more and more rods to calculate the bigger numbers