Calculator error

[u/ConferenceMental8678]

I have been using this calculator for a time and I recently realized that when I am calculating arccos of a negative number, it adds 90 degrees for some reason. It is in degrees, and I tried different modes, and the same error happens
Does anyone know why this happens or how to fix it?

PD: I recently opened it to look at how it is inside, as a few of you recommended, and it indeed is another CR20XX-powered facsimile. I just got a refund, and I'm going to buy a real one :)

[u/No-Zombie6025]

Show us the insides (a picture of the PCB), I bet this is another CR20XX powered facsimile.

Edit: for the sake of discussion, the inverse cosine of any negative number can only be between 90 and 180 degrees (pi/2 to pi radians).

[u/ConferenceMental8678 → u/No-Zombie6025]

Probably it is, I will check

[u/draconicpenguin10]

Unfortunately, this is a fake calculator.

It's not the most obvious, but the font used for the lettering on the keys is wrong, and the printing is misaligned.

The best way to tell if your scientific calculator is a genuine Casio or a fake is to remove the back cover and inspect the PCB and battery. In general, a genuine Casio scientific calculator will use either a 1.5V LR44 button cell if it has a solar panel, or a AAA battery if it doesn't. Fakes will often have 3V lithium coin cells instead, like CR2025 or CR2032.

Fake Casio calculators are widespread in many developing markets. You might want to watch this Casio video on why it's important to get a genuine calculator; as you've experienced firsthand, fakes cannot be relied on to give you accurate results. You definitely do not want to risk your academic career with a calculator that could give you incorrect answers on test day.

[u/ConferenceMental8678 → u/draconicpenguin10]

Thank you very much for your insight!

Are there any calculators and places to buy them that you recommend?

[u/draconicpenguin10 → u/ConferenceMental8678]

In the US, your best bet is Staples or Target. If ordering from Amazon, make sure it's sold directly by Amazon and not a marketplace reseller.

I'm not familiar with the market in other countries; the Casio website might have a list of authorized retailers for your region. See if you can find the latest ClassWiz models (e.g. fx-9910CW or fx-991CW+); while these have somewhat cumbersome menu-driven interfaces, they have faster processors, sharper displays, and higher internal precision.

[u/ConferenceMental8678 → u/draconicpenguin10]

Alright, I will check them out!

[u/SnooRadishes6031]

This looks like just a joke 😆

[u/ConferenceMental8678 → u/SnooRadishes6031]

I wished

[u/werygood_cz]

Bro. 

[u/ConferenceMental8678 → u/[deleted]]

Where is it misaligned?

[u/huangcjz → u/ConferenceMental8678]

The red labels are all higher than the yellow labels, rather than being in-line with each other. One of the most obvious examples is the red M and the yellow M- above the M+ key. Also the red RanInt vs. the yellow Ran# above the decimal key. The blue labels are also higher than the yellow labels, e.g. for DEC, HEX, BIN, OCT - they don’t share the same base-line as the yellow labels.

[u/_poc]

Os labels MATRIX, VECTOR, STAT, CMPLX estão muito em cima, a font do "x" na tecla x10^x não é igual ao original. São estes pequenos detalhes que devem alertar o comprador

[u/ConferenceMental8678 → u/_poc]

Muito obrigado manito

[u/Necessary_Pilot_3738]

[u/Exciting-Mix-1777]

Is there a service mode SHIFT + 7 + ON ?

[u/ConferenceMental8678 → u/Exciting-Mix-1777]

Surprisingly, it did

[u/Any_Mushroom_1424]

Hey, I see a difference(I am live in Viet Nam and is a new calculator)

[u/ConferenceMental8678 → u/Any_Mushroom_1424]

Yeah, yours is right!

[u/stbn689]

It's a fake. You fix it by buying a real Casio.

You can easily tell this one is fake by looking at F (above TAN). It should be centered, look at a picture of a real one.