I don't have one in front of me, but according to the Festool website a sys1 is 395mm x 295mm
therefore the square root of (395 x 395) + (295 x 295) = 493 which is about 19 3/8"
I only mention this because my answer is so far from the one you posted (and because work is very slow today!)
I took the outside measurements whereas I presume you took the inside measurements.