Section 6: Functions continue99
Keystrokes Display
1.49 ENTER
 1.49

0.015  ÷
 99.3333

1.94 ENTER
 1.94

.67 g Yx
 1.5589

×
 154.854

38 SIN
 0.6157

2 1/x
 0.5

g Yx
 0.7846

×
 121.505
The flow over the spillway is about 122 cubic feet per second, easy swimming for the average salmon in this spillway.
g CLX
 – 0

###### Statistical Functions
Accumulations
Executing the The Σ+ function automatically gives several different sums and products of the values in the X- and Y-registers at once. In order to make these values accessible for sophisticated statistics problems, they are automatically placed by the calculator into a block of six storage registers that you define with the ΣREG function.
When you execute ΣREG , the HP-41C prompts you for a register address with ΣREG _ _ The address you specify defines the beginning of a block of six statistical registers.
If you have not specified a block of statistical registers using the ΣREG function, the statistical registers will automatically be R11 through R16. But if you change the location of the statistical registers, that change remains in effect until you change it again, even while the HP-41C is off.
Before you begin any calculations using the Σ+ key, you should first clear the storage registers used in accumulations by executing the CLΣ (clear statistical registers) function.
When you key in a number and press the Σ+ key, the calculator performs each of the following operations:
 1. The number in the X-register is added to the contents of the first statistical register (the first statistical register is presently defined as R11). 2. The square of the number in the X-register is added to the contents of the second statistical register (presently defined as R12). 3. The number in the Y-register of the stack is added to the contents of the third statistical register (presently defined as R13).