David Connearn draws lines like these, and has been doing for 18 years. You might well draw the line at calling it art. But then, nobody's perfect.

I think you can see what's going on. Across the top of the page he draws a straight line, freehand, left to right - or he tries to, but inevitably the line wanders slightly from true. Just under it he draws another line, not straight now, but a line that follows the wandering path of the first, or tries to. Just under that he draws a third line which follows the path of the second, or tries to. And so on. Each line aims to hug the contour of the last, but each line errs and veers off its intended track, converging with or diverging from the line above, and setting a new track for the next. The drawing unfolds as a Chinese whisper of imperfectly echoed lines relaying down the page.

This is David Connearn's work and these are the rules he follows, in drawings made in various sizes and shapes, usually rectangular. It's the kind of work he now has hanging in Inverness, the opening show at the just-renovated and not so happily renamed Art TM gallery (Highland Printmakers as was) overloooking a straight stretch of the rushing Ness river. Those who know his work won't be in for a complete surprise. Connearn is 45, he developed this working method 18 years ago, and he's held to it ever since. For the viewer, too, a little patience is what's going to be rewarded.

A picture-seeking eye can pick-up inklings in these drawings - of rock strata, say, or a cloth weave, or a high aerial view of the ocean, or a seismographic print-out. And certainly what I like about them first of all is, not exactly their pictures, but their textures, the beautiful and mysterious variable densities - the way the grain spreads and concentrates in brighter and darker layers, disturbances start, proliferate, settle, disperse, forming wrinkles, incisions, stocking-ladders, waves, eddies and knots. The drawing on this page is more or less actual size. In larger works, these ravelling rhythms build to a great and greatly absorbing richness: force-fields, massive weights, shimmering veils. But I see there's something odd about treating these drawings as any sort of image, picture or pattern, because their effects are, in a way, quite unintended.

To be sure, it isn't "automatic" drawing, in the Surreal sense, and it isn't ungoverned chance. Connearn has his rules and keeps to them. He decides the dimension and format of a drawing, he chooses the nib-width. He knows the kind of effects his procedure produces. But, as for the particular appearance of each work, that's not within his grasp. The textures are determined by the successive, minute, accumulating meanderings of each stroke. The edges result from the small misalignments of each line's beginning and end. A drawing produces itself, a series of reflexive responses, a controlled loss of control.

If the process is peculiar, it's peculiar in its extremism. It takes some general truths about drawing, and makes them absolute. It's common enough to say that all drawing, as well as being image-making, is also the record of an activity in time, a sequence of actions and gestures. But Connearn's drawing is explicitly sequenced, it runs left to right and top to bottom, line by line; and it's all activity, done with no view to the picture as a whole, which is purely a by-product. The image materialises without any plan. You follow it down, through its various layers of closely and widely spaced lines, and what you're following isn't a pattern but some variation in the drawer's attention or tempo.

It's true, too, that freehand drawing is never fully deliberate. A drawn line isn't plotted like the line of a graph. Every stroke is a kind of throw. But Connearn's drawing lets this letting-go make all the going. Each line is drawn steadily, but without a pause and without correction. What happens, happens. What makes each line distinct, different from the last when it is trying to be the same, is simply that the hand can't help it. It can't exactly repeat its last action. Take the diagonal ripples that descend left to right in all the drawings. This diagonal is an occupational hazard. A wiggle gets into a line. But when it comes to be echoed in the next line, the hand's reaction is slightly delayed. The next wiggle comes out a bit to the right, and so on down.

So this system is a study in error. It generates it and makes it visible. It sets up a situation where human error is released from human design. Yet, if the errors can't be eliminated, they can to an extent be calculated. The main drawings in this show (called Time and Tide) do that. They come in two sets of three, long upright oblongs, and they're a departure in that they are made with a view to the image as a whole; in fact they have a kind of subject - the river outside the gallery window, a tidal river that rises and falls.

There's some reflection of this tide-turn in the way Connearn has controlled his diagonal ripples. In the right-hand picture, they fall as usual, left to right. But in the left-hand one, they fall the other way, right to left, got by drawing the lines from right to left, so the delayed response occurs in the opposition direction. In the central one, they run down vertically, got by drawing the lines alternately left-right and right- left.

By now I sense that the patience of some readers will be straining. And pointing out that Connearn's procedure, though constant, actually affords a great deal of variety will, I know, only further provoke. So the ripples can be made to go the other way! Big deal! What kind of a way is this to carry on? And for 18 years? Surely there's a mad pedantry in a method specifically devised to trap and exhibit one's own wandering hand. Surely this unending, insoluble game of solitaire is the wilful pursuit of futility. And, even given that his drawing-method has a general metaphorical force - exemplary of how any of life's patterns is an accumulation of errors - wouldn't a single drawing or a handful have made the point?

Certainly, one can't attend to this work for long without thinking about the state of mind involved in drawing these thousands of lines, over and over, year on year. I too don't really understand the need, though one needn't call it obsessional. I do see that, from a certain point of view, having started on this course there would never be any reason to stop, because there's no end in view. Stopping would be an arbitrary decision. But then, just as life is full of error, it's also full of arbitrariness, so there would be a truth there too, and the fact that Connearn's drawings do start and stop on arbitrary plans already compromises their impulse to endless- ness. And, while the process is indeed capable of infinite, inexhaustible variation, so is any process. It might stop. It doesn't.

You find in the end that you are looking two ways. One way you have an extraordinary body of evidence, human products that work on barely human terms, exercises beyond the will's ambit, that register and stress the human only as an irreducible inefficiency. The other, you have the off-cuts of an ongoing drive or commitment or calling (whatever you want to call it) which, though it can become a spectacle in itself, is really not your business. Not art then? No, no. And you think you could do it yourself? Well, of course you could - and perhaps the best way into this work isn't to look but to try.

To 7 March, Art TM, 20 Bank Street, Inverness.