HP 35s Manual page 4

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HP 35s Using Register Arithmetic
Answer: The mass of the Moon is now in register M, the mass of the Earth is in register E, and the mass of the
Earth-Moon twin system is in register T. The mass of the Earth is also still in the current register, as shown
in Figure 2. To confirm that the number in register T is the sum of the two masses, view register T by
pressing:
¹ÈT
In RPN mode, the STO+ command adds the current number to the register selected by its name, STO- subtracts the
current number from the named register, STO× multiplies the named register by the current number and STO÷ divides
the named register by the current number. In all these cases in RPN mode, the number itself is unchanged and
continues to be the current number. As it has not changed, the value in the LastX register also remains unchanged.
Practice Example: Calculating Using RCL Arithmetic in RPN mode
Example 2: If the Earth-Moon system is called a twin system, the mass of the Moon should be fairly similar to the mass
of the Earth. How do they compare?
Solution: The mass of the Earth is still in the current register. Recall the mass of the Moon from register M and divide
it into the current register. Press these keys.
h¯M
The result of the division is now in the current register.
Answer: The ratio of the masses of the Earth and the Moon is about 1:81. The Moon's mass is only about 1.2% that
of the Earth's, not really a twin. Nevertheless, the two are much closer in mass than any other major planet-
satellite system. For example the mass of Ganymede is 0.0078% of the mass of Jupiter, and the mass of
Deimos is 0.0000017% of the mass of Mars. Only Charon and Pluto are closer, with Charon having about
15% of the mass of Pluto – and not all planetary scientists are willing to consider Pluto to be a planet.
In RPN mode, when h is pressed, followed by an arithmetic operation and a letter, then the number in the chosen
register is recalled and added to, subtracted from, multiplied by, or divided into, the current register. As opposed to STO
arithmetic, RCL arithmetic changes the current number and leaves the stored number unchanged. Because the current
number is changed, its previous value is stored in the LastX register for re-use in RPN mode.
Storage Arithmetic in a Program
As these examples show, STO and RCL arithmetic make some calculations easier to carry out. It is generally quicker to
use a STO or RCL arithmetic operation rather than to RCL a number, calculate with it, and then STO the result. Quite
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Figure 5
Figure 6
- 4 - HP 35s Using Register Arithmetic - Version 1.0