So don't insist on precise writing, but do insist on clear writing. You'll be surprised at how good the writing turns out to be. They want to be reassured that they will be adequately prepared for courses which follow and use calculus. Students have plenty of chance to show ingenuity in their work on the Give it a Try assignments. Tests and quizzes should deal with matters of calculus literacy.
Quizzes are also useful for the students to help in perfecting their hand skills.
Problems for tests and quizzes should be lifted off the Literacy Sheets. Light modification of these problems is fine. Short quizzes should be constructed to signal to the student serious gaps that must be filled. Some instructors teaching a five hour course find it benefical to give quizzes on a day other than Wednesdays, thus reserving Wednesdays for discussions only. These tests are given in classrooms away from the machines.