casio fx-451m

a very popular scientific wallet folding calculator from the 80's. a 10+2 digit lcd with c-power, which is a combination of solar and a gr927 lithium battery (like the fx-992v).

the innovative design has an additional 32 buttons inside the cover. the buttons operate by touch and make the unit slightly awkward to operate when held by one hand. a weakness of the design is that, after prolonged use, the internal edge connections can fail and the spin can sometimes split. hp came up with a much more elegant way to implement this with their 28c and later models.

nevertheless, the idea provides space for many useful features otherwise not so well accommodated. one such feature is the extensive collections of physical constants and unit conversions.

altogether a very compact and functional unit.


one of the problems in offering physical constants is that they change. for example, these ones are based on a standard from 1978 and since then, some have been redefined. for example na (avogadro's constant) is given as 6.022045e23, but it is now 6.022142e23, a relative difference of 16ppm. another glitch is that 1000g -> oz/16 (lb) -> Kg = 1+0.82e-6, showing the internal conversions constants arent quite in agreement.