Step 2, enter *300 1# 12345#* on the dial, and then press the call button, and the field application is built into iOS. The test starts, and at the same time, the accurate value of signal strength appears in the upper left corner;

Step three, hold it down? iPhone？ Turn on the key (that is, the top power key) until the "slide off" slider appears;

Step 4, finally press and hold the Home button until the power-off slider disappears, and the machine will return to the main screen interface;

Step 5: At this time, the signal strength value will always be displayed in the upper left corner of the iPhone screen, and you can click it to switch between digital and signal grid.

Extended data

Screen and camera iPhone includes the media playback function of iPod, the modified Mac OS X operating system (iOS, real name iPhone OS, renamed as iOS since version 4.0) for mobile devices, and an 8-megapixel camera.

(First and second generation 2 million, 3GS 320 million, support autofocus. The fourth generation has been upgraded to back-illuminated 5 million, while the 4S released by 20 1 1 has been upgraded to 8 million, with a large aperture of 2.4f In addition, the device has a built-in gravity sensor, and the iPhone4 has a three-axis gyroscope (three-axis direction gravity sensor), which can be adjusted horizontally or vertically according to the user.

And the built-in light sensor supports adjusting the screen brightness according to the current light intensity. There is also a built-in distance sensor to prevent the operation caused by the ear touching the screen by mistake when answering the phone. IPhone4S and 5 released in September, 20 12 added a brand-new camera mode-panoramic mode, which can be used to take panoramic photos, and the panoramic photos can reach 28 million pixels.