How to Tell Time With Your Hand, 1633

Pocket Sundial, c. 1640
Harvard University

"[T]o see onely by the hand what of the clocke it is...  may bee practiced by the left hand in this manner. Take a straw or like thing of the length of the Index, or the second finger, hold this straw very right betweene the thumbe and the right finger, then stretch forth the hand and turne your backe and the palme of your hand towards the Sunne; so that the shaddow of the muscle which is under the thumbe touch the line of life, which is betweene the middle of the two other great lines, which is seene in the palme of the hand; this done, the end of the shaddow will shew what of the clocke it is; for at the end of the great finger it is 7 in the morning or 5 in the evening; at the end of the Ring finger it is 8 in the morning, or 4 in the evening; at the end of the little finger or first joynt, it is 9 in the morning, or 3 in the afternoone; 10 and 2 at the second joynt, 11 and 1 at the third joynt, and midday in the line following, which comes from the end of the Index." 

Hendrik van Etten, Mathematicall Recreations (1633)

In theory, this ingenious method will allow you to tell time using only a straw. But you'll be lucky if you manage to calculate the time before the sun sets, and you may inadvertently offend passersby with your finger gestures.