this is the first time I'm making a PCB layout, so I'm not too familiar with datasheets. The picture below shows a diagram for an IC I'm using. The datasheet says all dimensions are in mm. However, near the bottom you can see a number that has 0.25 with a circled M, followed by an A and C. What do these letters mean? And does that mean the hole size is 0.25 mm for a pin? I'm really confused because I know it can't be 0.25mm. Is that in mils instead?