This keyboard was made for NEC PC9801VX(80286 8/10MHz) , PC9801vm(V30 10MHz), PC9801M(8086), PC9801F(8086), and PC9801E(8086) series in 1980's. I had PC9801VX2 in the past (I bought it at 1986, it cost $4000). The blue switch needs 260g to push. It is assigned to STOP key, and is equivalent to CTRL+C. The later 80386 model has 15 functions keys (vf.1 ~ vf.5 are at the above of the ten keys). The switch is NEC original.