How to do a screengrab in Tab 2 7in

Apple did it perfectly on the original Ipad 1. It is strange that my Samsung Tab 2 7in cannot do it consistently.In the latter tablet, you press the power button then the volume Down control button and hold them long enough until a notification "Copied to Clipbboard" or "Saving Screenshot" appears that you have saved the screen to the clipboard,

Yesterday night, that appears to be working, but as I write this, the key presses do not work! That key press combintation turned off the tablet! Ah well, enough for us to record our failure... If any reader has a consistent mathod to do a screen grab, please tell us how to do it in the comments. Thank you.

If at first it does not work within 2 seconds, RELEASE then REDO.

July 4, 2013.

It seemed to work again. The image is saved to the clipboard.The files are stored under the directory /storage/sdcard0/Pictures/Screenshots.