You ARE allowed to measure a space with your hand and that allowance might extend to your cue (though if faced with this situation, you might want to ask the referee first).
You may only use your vision to judge whether the cue ball or an object ball would fit through a gap, or to judge what ball the cue ball would contact first. You may not use any ball, cue, rack, or any other equipment or other part of your body as a width-measuring device. (AR p. 73).
Penalty for (f-g): Foul immediately upon the violation, regardless of
whether a shot is executed.
I've seen SVB measure an OB's distance from the rail with his cue when calculating a rail-first kick shot (double-the-distance method). No one at the tournament said anything about it.
BCA rules
Use of Equipment, 1-3 g.
To be clear, these aren't the "BCA Rules". These are the BCA League Rules. I know it sounds silly but there's a difference.
You're right. I changed it in my original post.
I've seen SVB measure an OB's distance from the rail with his cue when calculating a rail-first kick shot (double-the-distance method). No one at the tournament said anything about it.
Yea I was gambling with someone last night and we weren't playing specific BCA rules but I'm down shooting the 8 ball and he comes up to the table, grabs a ball out of the pocket and puts it in front of the 8 "to see if it would go". I told him he is more than welcome to get someone to watch a hit but that he couldn't take balls out of the pocket as a measuring device, especially when I'm shooting. I was just curious to the rule as I play a lot of one pocket also.
Yea I was gambling with someone last night and we weren't playing specific BCA rules but I'm down shooting the 8 ball and he comes up to the table, grabs a ball out of the pocket and puts it in front of the 8 "to see if it would go". I told him he is more than welcome to get someone to watch a hit but that he couldn't take balls out of the pocket as a measuring device, especially when I'm shooting. I was just curious to the rule as I play a lot of one pocket also.