I am teaching myself digital electronics by working through the exercises in the second half of Student Manual for The Art of Electronics. I have encountered a problem that has left me totally befuddled: in section 19-4 (see attached image), I need to wire some circuitry to control output to a data display. The data displays have latches, so that in order to actually display the value being input at any point in time, pin 5 needs to be low. The input to pin 5 of the left two data displays comes from pin 8 of the HCT10 (see highlighted part of attached image), which is a 3-input NAND gate. And heres where the weirdness comes in: in my circuit, Ive measured the three inputs (to pins 9, 10, and 11) to all be high, which means the output from pin 8 of the HCT10 should be low. When I measure pin 8, it is lowUNTIL I connect pin 8 of the HCT10 to pin 5 of the data display. Then it goes HIGH! Clearly the output from the HCT10 should not depend on where I connect it, and yet that is definitely what is happening, and its preventing the data display from working as it is supposed to. Im guessing theres something Im not understanding about whats going on inside the guts of the HCT10. Any help would be much appreciated. Thanks.